diff --git a/backend/src/__tests__/scheduled-tasks-routes.test.ts b/backend/src/__tests__/scheduled-tasks-routes.test.ts
index 072d31f3..92fda6f5 100644
--- a/backend/src/__tests__/scheduled-tasks-routes.test.ts
+++ b/backend/src/__tests__/scheduled-tasks-routes.test.ts
@@ -224,6 +224,60 @@ describe('POST /api/scheduled-tasks', () => {
     expect(res.body.cron_expression).toBe('@daily');
   });
 
+  it('pins next_run_at to an explicit one-shot run_at instead of the cron-derived next run', async () => {
+    // A one-shot for next year: the cron (0 23 1 7 *) would otherwise resolve to
+    // this year's occurrence. run_at must win so the task fires on the chosen year.
+    const runAt = new Date(new Date().getFullYear() + 1, 6, 1, 23, 0, 0, 0).getTime();
+    const res = await request(app).post('/api/scheduled-tasks').set('Cookie', adminCookie).send({
+      ...basePayload, cron_expression: '0 23 1 7 *', delete_after_run: true, run_at: runAt,
+    });
+    expect(res.status).toBe(201);
+    expect(res.body.next_run_at).toBe(runAt);
+  });
+
+  it('falls back to the cron-derived next run when no run_at is supplied', async () => {
+    const res = await request(app).post('/api/scheduled-tasks').set('Cookie', adminCookie).send({
+      ...basePayload, cron_expression: '0 3 * * *',
+    });
+    expect(res.status).toBe(201);
+    // Cron-derived next run is some future instant, not pinned to a passed timestamp.
+    expect(typeof res.body.next_run_at).toBe('number');
+    expect(res.body.next_run_at).toBeGreaterThan(Date.now());
+  });
+
+  it('rejects a run_at in the past with 400', async () => {
+    const res = await request(app).post('/api/scheduled-tasks').set('Cookie', adminCookie).send({
+      ...basePayload, cron_expression: '0 23 1 7 *', delete_after_run: true, run_at: Date.now() - 60_000,
+    });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/run_at must be in the future/);
+  });
+
+  it('rejects a non-numeric run_at with 400', async () => {
+    const res = await request(app).post('/api/scheduled-tasks').set('Cookie', adminCookie).send({
+      ...basePayload, cron_expression: '0 23 1 7 *', run_at: '2027-07-01',
+    });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/run_at must be an epoch-millisecond timestamp/);
+  });
+
+  it('rejects a fractional run_at with 400 (must be an integer epoch-ms)', async () => {
+    const res = await request(app).post('/api/scheduled-tasks').set('Cookie', adminCookie).send({
+      ...basePayload, cron_expression: '0 23 1 7 *', run_at: Date.now() + 100000.5,
+    });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/run_at must be an epoch-millisecond timestamp/);
+  });
+
+  it('ignores run_at for a disabled task (next_run_at stays null)', async () => {
+    const res = await request(app).post('/api/scheduled-tasks').set('Cookie', adminCookie).send({
+      ...basePayload, enabled: false, cron_expression: '0 23 1 7 *', delete_after_run: true,
+      run_at: new Date(new Date().getFullYear() + 1, 6, 1, 23, 0, 0, 0).getTime(),
+    });
+    expect(res.status).toBe(201);
+    expect(res.body.next_run_at).toBeNull();
+  });
+
   it('rejects unsupported actions', async () => {
     const res = await request(app).post('/api/scheduled-tasks').set('Cookie', adminCookie).send({
       ...basePayload, action: 'nuke',
@@ -417,6 +471,30 @@ describe('PATCH /api/scheduled-tasks/:id/toggle', () => {
     expect(on.body.enabled).toBe(1);
     expect(typeof on.body.next_run_at).toBe('number');
   });
+
+  it('preserves a one-shot pinned next_run_at across a disable/enable cycle', async () => {
+    const now = Date.now();
+    // A one-shot pinned to next year (its yearless cron would resolve to this year).
+    const pinned = new Date(new Date().getFullYear() + 1, 6, 1, 23, 0, 0, 0).getTime();
+    const id = DatabaseService.getInstance().createScheduledTask({
+      name: 'once', target_type: 'stack', target_id: 's', node_id: 1, action: 'auto_backup',
+      cron_expression: '0 23 1 7 *', enabled: 1, created_by: 'admin', created_at: now, updated_at: now,
+      last_run_at: null, next_run_at: pinned, last_status: null, last_error: null,
+      prune_targets: null, target_services: null, prune_label_filter: null, delete_after_run: 1,
+    });
+
+    const off = await request(app).patch(`/api/scheduled-tasks/${id}/toggle`).set('Cookie', adminCookie);
+    expect(off.status).toBe(200);
+    expect(off.body.enabled).toBe(0);
+    // The pinned instant survives the disable so it can be restored on re-enable.
+    expect(off.body.next_run_at).toBe(pinned);
+
+    const on = await request(app).patch(`/api/scheduled-tasks/${id}/toggle`).set('Cookie', adminCookie);
+    expect(on.status).toBe(200);
+    expect(on.body.enabled).toBe(1);
+    // Re-enable restores the exact chosen instant, not the cron's annual occurrence.
+    expect(on.body.next_run_at).toBe(pinned);
+  });
 });
 
 describe('DELETE /api/scheduled-tasks/:id', () => {
@@ -582,6 +660,41 @@ describe('PUT /api/scheduled-tasks/:id - delete_after_run', () => {
     expect(res2.status).toBe(200);
     expect(res2.body.delete_after_run).toBe(0);
   });
+
+  it('pins next_run_at to a re-supplied one-shot run_at on update', async () => {
+    const now = Date.now();
+    const id = DatabaseService.getInstance().createScheduledTask({
+      name: 'once', target_type: 'stack', target_id: 's', node_id: 1, action: 'auto_backup',
+      cron_expression: '0 23 1 7 *', enabled: 1, created_by: 'admin', created_at: now, updated_at: now,
+      last_run_at: null, next_run_at: now + 1000, last_status: null, last_error: null,
+      prune_targets: null, target_services: null, prune_label_filter: null, delete_after_run: 1,
+    });
+
+    const runAt = new Date(new Date().getFullYear() + 1, 6, 1, 23, 0, 0, 0).getTime();
+    const res = await request(app)
+      .put(`/api/scheduled-tasks/${id}`)
+      .set('Cookie', adminCookie)
+      .send({ cron_expression: '0 23 1 7 *', run_at: runAt });
+    expect(res.status).toBe(200);
+    expect(res.body.next_run_at).toBe(runAt);
+  });
+
+  it('rejects an update with a past run_at', async () => {
+    const now = Date.now();
+    const id = DatabaseService.getInstance().createScheduledTask({
+      name: 'once', target_type: 'stack', target_id: 's', node_id: 1, action: 'auto_backup',
+      cron_expression: '0 23 1 7 *', enabled: 1, created_by: 'admin', created_at: now, updated_at: now,
+      last_run_at: null, next_run_at: now + 1000, last_status: null, last_error: null,
+      prune_targets: null, target_services: null, prune_label_filter: null, delete_after_run: 1,
+    });
+
+    const res = await request(app)
+      .put(`/api/scheduled-tasks/${id}`)
+      .set('Cookie', adminCookie)
+      .send({ run_at: Date.now() - 60_000 });
+    expect(res.status).toBe(400);
+    expect(res.body.error).toMatch(/run_at must be in the future/);
+  });
 });
 
 describe('PUT /api/scheduled-tasks/:id - stack target validation', () => {
diff --git a/backend/src/routes/scheduledTasks.ts b/backend/src/routes/scheduledTasks.ts
index cc708ee3..935b219a 100644
--- a/backend/src/routes/scheduledTasks.ts
+++ b/backend/src/routes/scheduledTasks.ts
@@ -163,6 +163,25 @@ function validateCronExpression(cron: unknown): string | null {
   return null;
 }
 
+/**
+ * Validate the optional explicit fire time. When present it must be a future
+ * epoch-ms integer; absent (undefined/null) leaves the cron-derived next run in
+ * place. By convention only a one-time ('once') schedule populates run_at (the
+ * frontend's getOnceRunAt), because a 5-field cron has no year field and the
+ * cron alone would fire on the next annual occurrence rather than the exact date
+ * the admin chose; this validator itself only checks shape and futureness.
+ */
+function validateRunAt(runAt: unknown): string | null {
+  if (runAt === undefined || runAt === null) return null;
+  if (typeof runAt !== 'number' || !Number.isInteger(runAt)) {
+    return 'run_at must be an epoch-millisecond timestamp.';
+  }
+  if (runAt <= Date.now()) {
+    return 'run_at must be in the future.';
+  }
+  return null;
+}
+
 export const scheduledTasksRouter = Router();
 
 scheduledTasksRouter.get('/', (req: Request, res: Response): void => {
@@ -201,7 +220,7 @@ scheduledTasksRouter.get('/', (req: Request, res: Response): void => {
 scheduledTasksRouter.post('/', (req: Request, res: Response): void => {
   if (!requireAdmin(req, res)) return;
   try {
-    const { name, target_type, target_id, node_id, action, cron_expression, enabled, prune_targets, target_services, prune_label_filter, delete_after_run } = req.body;
+    const { name, target_type, target_id, node_id, action, cron_expression, enabled, prune_targets, target_services, prune_label_filter, delete_after_run, run_at } = req.body;
 
     if (!name || typeof name !== 'string' || !name.trim()) {
       res.status(400).json({ error: 'Name is required' }); return;
@@ -227,9 +246,16 @@ scheduledTasksRouter.post('/', (req: Request, res: Response): void => {
     const cronErr = validateCronExpression(cron_expression);
     if (cronErr) { res.status(400).json({ error: cronErr }); return; }
 
+    const runAtErr = validateRunAt(run_at);
+    if (runAtErr) { res.status(400).json({ error: runAtErr }); return; }
+
     const scheduler = SchedulerService.getInstance();
     const now = Date.now();
-    const nextRun = (enabled !== false) ? scheduler.calculateNextRun(cron_expression) : null;
+    // A one-shot's run_at pins the exact instant (including year); fall back to
+    // the cron-derived next run when no explicit timestamp is supplied.
+    const nextRun = (enabled === false)
+      ? null
+      : (typeof run_at === 'number' ? run_at : scheduler.calculateNextRun(cron_expression));
     const normalizedTargetId = target_type === 'stack' ? target_id : null;
     const normalizedNodeId = actionRequiresNode(action) ? parsePositiveNodeId(node_id) : null;
 
@@ -288,7 +314,7 @@ scheduledTasksRouter.put('/:id', (req: Request, res: Response): void => {
     const existing = db.getScheduledTask(id);
     if (!existing) { res.status(404).json({ error: 'Scheduled task not found' }); return; }
 
-    const { name, target_type, target_id, node_id, action, cron_expression, enabled, prune_targets, target_services, prune_label_filter, delete_after_run } = req.body;
+    const { name, target_type, target_id, node_id, action, cron_expression, enabled, prune_targets, target_services, prune_label_filter, delete_after_run, run_at } = req.body;
 
     if (target_type !== undefined && !(VALID_TARGET_TYPES as readonly string[]).includes(target_type)) {
       res.status(400).json({ error: 'Invalid target_type' }); return;
@@ -322,6 +348,9 @@ scheduledTasksRouter.put('/:id', (req: Request, res: Response): void => {
       if (cronErr) { res.status(400).json({ error: cronErr }); return; }
     }
 
+    const runAtErr = validateRunAt(run_at);
+    if (runAtErr) { res.status(400).json({ error: runAtErr }); return; }
+
     const updates: Partial<Omit<ScheduledTask, 'id'>> = { updated_at: Date.now() };
     if (name !== undefined) {
       if (typeof name !== 'string' || !name.trim()) {
@@ -359,7 +388,11 @@ scheduledTasksRouter.put('/:id', (req: Request, res: Response): void => {
     const finalCron = cron_expression || existing.cron_expression;
     const finalEnabled = enabled !== undefined ? enabled : existing.enabled;
     if (finalEnabled) {
-      updates.next_run_at = SchedulerService.getInstance().calculateNextRun(finalCron);
+      // A re-supplied one-shot run_at pins the exact instant; otherwise recompute
+      // from the (possibly updated) cron.
+      updates.next_run_at = typeof run_at === 'number'
+        ? run_at
+        : SchedulerService.getInstance().calculateNextRun(finalCron);
     } else {
       updates.next_run_at = null;
     }
@@ -406,7 +439,19 @@ scheduledTasksRouter.patch('/:id/toggle', (req: Request, res: Response): void =>
     if (!existing) { res.status(404).json({ error: 'Scheduled task not found' }); return; }
 
     const newEnabled = existing.enabled ? 0 : 1;
-    const nextRun = newEnabled ? SchedulerService.getInstance().calculateNextRun(existing.cron_expression) : null;
+    // A one-shot's exact instant cannot be reconstructed from its yearless cron,
+    // so preserve its pinned next_run_at across a disable/enable cycle (the
+    // enabled=0 gate stops a disabled task from firing). Recurring tasks clear
+    // next_run_at while disabled and recompute it from the cron on enable.
+    const isOneShot = existing.delete_after_run === 1 && existing.next_run_at != null;
+    let nextRun: number | null;
+    if (isOneShot) {
+      // The pinned instant is kept in both directions: disabling leaves it set
+      // (the enabled=0 gate stops it firing) so re-enabling restores it.
+      nextRun = existing.next_run_at;
+    } else {
+      nextRun = newEnabled ? SchedulerService.getInstance().calculateNextRun(existing.cron_expression) : null;
+    }
 
     db.updateScheduledTask(id, {
       enabled: newEnabled,
diff --git a/frontend/src/components/ScheduledOperationsView.tsx b/frontend/src/components/ScheduledOperationsView.tsx
index b8d87aec..07f432fb 100644
--- a/frontend/src/components/ScheduledOperationsView.tsx
+++ b/frontend/src/components/ScheduledOperationsView.tsx
@@ -22,6 +22,7 @@ import {
   buildCron,
   parseCron,
   getSimpleScheduleError,
+  getOnceRunAt,
   type SimpleSchedule,
 } from '@/lib/scheduling';
 import { ScheduleSimplePanel } from './ScheduleSimplePanel';
@@ -277,6 +278,11 @@ export default function ScheduledOperationsView({ filterNodeId, onClearFilter, p
     // backend stores; Advanced mode sends the raw expression as-is.
     const cronExpression = scheduleMode === 'simple' ? buildCron(simpleSchedule) : formCron;
 
+    // A one-time ('once') Simple schedule pins its exact run instant (including
+    // year) via run_at, because the 5-field cron cannot encode a year. null for
+    // every recurring shape and for Advanced mode, where the cron is authoritative.
+    const runAt = scheduleMode === 'simple' ? getOnceRunAt(simpleSchedule) : null;
+
     const body: Record<string, unknown> = {
       name: formName,
       target_type: actionDef.targetType,
@@ -284,6 +290,7 @@ export default function ScheduledOperationsView({ filterNodeId, onClearFilter, p
       cron_expression: cronExpression,
       enabled: formEnabled,
       delete_after_run: formDeleteAfterRun,
+      run_at: runAt,
       target_id: actionDef.requiresStack ? formTargetId : null,
       node_id: actionDef.requiresNode && formNodeId ? parseInt(formNodeId, 10) : null,
       prune_targets: formAction === 'prune' && formPruneTargets.length > 0 ? formPruneTargets : null,
diff --git a/frontend/src/lib/scheduling.test.ts b/frontend/src/lib/scheduling.test.ts
index bd5182e2..04cb6cfb 100644
--- a/frontend/src/lib/scheduling.test.ts
+++ b/frontend/src/lib/scheduling.test.ts
@@ -4,6 +4,7 @@ import {
   buildCron,
   parseCron,
   getSimpleScheduleError,
+  getOnceRunAt,
   type SimpleSchedule,
 } from './scheduling';
 
@@ -140,6 +141,24 @@ describe('parseCron', () => {
   });
 });
 
+describe('getOnceRunAt', () => {
+  it('returns the exact picked instant (date + chosen time) for a once schedule', () => {
+    const runAt = getOnceRunAt(schedule({ frequency: 'once', minute: 30, hour: 23, date: new Date(2027, 6, 1) }));
+    expect(runAt).toBe(new Date(2027, 6, 1, 23, 30, 0, 0).getTime());
+  });
+
+  it('preserves the selected year so a future-year once does not collapse to this year', () => {
+    const runAt = getOnceRunAt(schedule({ frequency: 'once', minute: 0, hour: 9, date: new Date(2030, 0, 15) }));
+    expect(new Date(runAt as number).getFullYear()).toBe(2030);
+  });
+
+  it('returns null for a once schedule with no date and for recurring frequencies', () => {
+    expect(getOnceRunAt(schedule({ frequency: 'once', date: null }))).toBeNull();
+    expect(getOnceRunAt(schedule({ frequency: 'daily' }))).toBeNull();
+    expect(getOnceRunAt(schedule({ frequency: 'monthly', dayOfMonth: 5 }))).toBeNull();
+  });
+});
+
 describe('getSimpleScheduleError', () => {
   const now = new Date(2026, 5, 28);
 
@@ -162,13 +181,24 @@ describe('getSimpleScheduleError', () => {
 
   it('blocks once with a past date', () => {
     expect(getSimpleScheduleError(schedule({ frequency: 'once', date: new Date(2026, 5, 1) }), now))
-      .toBe('The selected date is in the past and this schedule would never fire.');
+      .toBe('The selected date and time are in the past and this schedule would never fire.');
   });
 
   it('passes once with a future date', () => {
     expect(getSimpleScheduleError(schedule({ frequency: 'once', date: new Date(2026, 11, 25) }), now)).toBeNull();
   });
 
+  it('blocks once for a time earlier today that has already passed', () => {
+    const noon = new Date(2026, 5, 28, 12, 0);
+    expect(getSimpleScheduleError(schedule({ frequency: 'once', date: new Date(2026, 5, 28), hour: 1, minute: 0 }), noon))
+      .toBe('The selected date and time are in the past and this schedule would never fire.');
+  });
+
+  it('passes once for a later time today that has not yet passed', () => {
+    const noon = new Date(2026, 5, 28, 12, 0);
+    expect(getSimpleScheduleError(schedule({ frequency: 'once', date: new Date(2026, 5, 28), hour: 23, minute: 0 }), noon)).toBeNull();
+  });
+
   it('blocks an invalid time', () => {
     expect(getSimpleScheduleError(schedule({ frequency: 'daily', minute: Number.NaN }), now)).toBe('Enter a valid time.');
   });
diff --git a/frontend/src/lib/scheduling.ts b/frontend/src/lib/scheduling.ts
index 6429dc34..77d506da 100644
--- a/frontend/src/lib/scheduling.ts
+++ b/frontend/src/lib/scheduling.ts
@@ -70,6 +70,19 @@ export function buildCron(s: SimpleSchedule): string {
   }
 }
 
+/**
+ * Absolute epoch-ms fire time for a one-time ('once') schedule: the picked date
+ * at the chosen hour and minute. Returns null when the schedule is not 'once' or
+ * has no date. A 5-field cron cannot encode a year, so a one-shot sends this
+ * explicit timestamp to the backend to pin the exact run (year and time of day);
+ * relying on the cron alone fires on the next annual occurrence, which can be a
+ * different year than the date the admin selected.
+ */
+export function getOnceRunAt(s: SimpleSchedule): number | null {
+  if (s.frequency !== 'once' || !s.date) return null;
+  return new Date(s.date.getFullYear(), s.date.getMonth(), s.date.getDate(), s.hour, s.minute, 0, 0).getTime();
+}
+
 function parseIntField(field: string, min: number, max: number): number | null {
   if (!/^\d+$/.test(field)) return null;
   const n = Number(field);
@@ -167,9 +180,14 @@ export function getSimpleScheduleError(s: SimpleSchedule, now: Date = new Date()
   }
   if (s.frequency === 'once') {
     if (!s.date) return 'Select a date.';
-    const picked = new Date(s.date.getFullYear(), s.date.getMonth(), s.date.getDate()).getTime();
-    const today = new Date(now.getFullYear(), now.getMonth(), now.getDate()).getTime();
-    if (picked < today) return 'The selected date is in the past and this schedule would never fire.';
+    // Compare the full chosen instant (date + time), not just the day: a time
+    // earlier today has already passed. The backend also rejects a past run_at
+    // with a 400; this is the friendlier, save-blocking guard surfaced before
+    // the request is sent.
+    const when = getOnceRunAt(s);
+    if (when !== null && when <= now.getTime()) {
+      return 'The selected date and time are in the past and this schedule would never fire.';
+    }
   }
   return null;
 }