diff --git a/eform-client/playwright/e2e/plugins/time-planning-pn/b/dashboard-edit-multishift.spec.ts b/eform-client/playwright/e2e/plugins/time-planning-pn/b/dashboard-edit-multishift.spec.ts
index 3c467e25c..245ec1ee6 100644
--- a/eform-client/playwright/e2e/plugins/time-planning-pn/b/dashboard-edit-multishift.spec.ts
+++ b/eform-client/playwright/e2e/plugins/time-planning-pn/b/dashboard-edit-multishift.spec.ts
@@ -245,4 +245,66 @@ test.describe('Dashboard — multi-shift (3-5) round-trip regression guard', ()
 
     await page.locator('#cancelButton').click();
   });
+
+  /**
+   * Regression guard for the "Use 1-minute intervals" first-user toggle in
+   * the Advanced settings section. The flag rides on AssignedSite end-to-end
+   * (entity → DTO → write mapping → angular model) and is persisted by
+   * TimeSettingService.UpdateAssignedSite. This test only verifies the UI
+   * plumbing — the toggle is dormant (no business-logic consumers yet).
+   *
+   * Gating: !data.resigned && (selectCurrentUserIsFirstUser$ | async).
+   * The CI seed logs in as admin@admin.com (LoginConstants.username), which
+   * is the first-user, so the toggle is visible in this test context.
+   */
+  test('first-user can toggle Use 1-minute intervals; persists across save+reopen', async ({ page }) => {
+    await page.locator('mat-nested-tree-node').filter({ hasText: 'Timeregistrering' }).click();
+    const indexPromise = page.waitForResponse(r =>
+      r.url().includes('/api/time-planning-pn/plannings/index') && r.request().method() === 'POST');
+    await page.locator('mat-tree-node').filter({ hasText: 'Dashboard' }).click();
+    await indexPromise;
+    await waitForSpinner(page);
+
+    // Open the assigned-site dialog for the third worker — same convention
+    // as the other tests on this shard so they don't clobber each other.
+    await page.locator('#firstColumn3').click();
+    await expect(page.locator('mat-dialog-container')).toBeVisible({ timeout: 10000 });
+
+    // The toggle is gated behind first-user; the CI fixture logs in as
+    // first-user, so it must be visible.
+    await expect(page.locator('#useOneMinuteIntervals')).toBeVisible({ timeout: 10000 });
+
+    const cb = page.locator('#useOneMinuteIntervals input[type="checkbox"]');
+    await cb.waitFor({ state: 'attached', timeout: 10000 });
+
+    // Capture the starting state, flip it, save, re-open, assert it persisted.
+    const wasChecked = await cb.isChecked();
+    await page.locator('#useOneMinuteIntervals').click({ force: true });
+    if (wasChecked) {
+      await expect(cb).not.toBeChecked();
+    } else {
+      await expect(cb).toBeChecked();
+    }
+
+    const assignSitePromise = page.waitForResponse(
+      r => r.url().includes('/api/time-planning-pn/settings/assigned-site') && r.request().method() === 'PUT');
+    await page.locator('#saveButton').click({ force: true });
+    await assignSitePromise;
+    await waitForSpinner(page);
+    await expect(page.locator('mat-dialog-container')).toHaveCount(0, { timeout: 10000 });
+
+    // Re-open and assert the new value round-tripped.
+    await page.locator('#firstColumn3').click();
+    await expect(page.locator('mat-dialog-container')).toBeVisible({ timeout: 10000 });
+
+    const cbReopened = page.locator('#useOneMinuteIntervals input[type="checkbox"]');
+    await cbReopened.waitFor({ state: 'attached', timeout: 10000 });
+    if (wasChecked) {
+      await expect(cbReopened).not.toBeChecked();
+    } else {
+      await expect(cbReopened).toBeChecked();
+    }
+
+    await page.locator('#cancelButton').click();
+  });
 });
diff --git a/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.html b/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.html
index 42705c957..a5861ec5f 100644
--- a/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.html
+++ b/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.html
@@ -224,6 +224,21 @@ <h3 class="section-header">{{ 'Employee status' | translate }}</h3>
           </mat-error>
         </mat-form-field>
       </div>
+
+      <!-- ========= Advanced settings (first-user only) ========= -->
+      <h3 class="section-header" *ngIf="!data.resigned && (selectCurrentUserIsFirstUser$ | async)">{{ 'Advanced settings' | translate }}</h3>
+
+      <div class="d-flex flex-row" *ngIf="!data.resigned && (selectCurrentUserIsFirstUser$ | async)">
+        <mat-checkbox class="p-1"
+                      [id]="'useOneMinuteIntervals'"
+                      [name]="'useOneMinuteIntervals'"
+                      formControlName="useOneMinuteIntervals">
+          <div>
+            <div>{{ 'Use 1-minute intervals' | translate }}</div>
+            <small class="checkbox-description">{{ 'Enable 1-minute granularity for time entry. Default increments are 5 or 15 minutes.' | translate }}</small>
+          </div>
+        </mat-checkbox>
+      </div>
     </mat-tab>
     <mat-tab label="{{'Plan hours' | translate }} "
              *ngIf="data.useOnlyPlanHours && selectCurrentUserIsFirstUser$ | async">
diff --git a/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.spec.ts b/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.spec.ts
index 18ed986fc..0270d19c5 100644
--- a/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.spec.ts
+++ b/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.spec.ts
@@ -565,4 +565,62 @@ describe('AssignedSiteDialogComponent', () => {
       }
     });
   });
+
+  describe('Use 1-minute intervals toggle', () => {
+    // The toggle's *ngIf gates on:
+    //   !data.resigned && (selectCurrentUserIsFirstUser$ | async)
+    // We follow the same no-`detectChanges` pattern adopted in PR #1538:
+    // assert against component state and observables, not the rendered DOM.
+    // Rendering the dialog under NO_ERRORS_SCHEMA hits the
+    // NG01203 "No value accessor for form control name: 'resigned'" issue
+    // because Material form-control directives aren't registered in the
+    // tested module.
+
+    function setupWithData(
+      overrides: Partial<typeof mockAssignedSiteData>,
+    ): AssignedSiteDialogComponent {
+      const data = { ...mockAssignedSiteData, ...overrides };
+      TestBed.resetTestingModule();
+      TestBed.configureTestingModule({
+        declarations: [AssignedSiteDialogComponent],
+        imports: [ReactiveFormsModule, TranslateModule.forRoot(), HttpClientTestingModule],
+        schemas: [NO_ERRORS_SCHEMA],
+        providers: [
+          FormBuilder,
+          { provide: MAT_DIALOG_DATA, useValue: data },
+          { provide: TimePlanningPnSettingsService, useValue: mockSettingsService },
+          { provide: TimePlanningPnPayRuleSetsService, useValue: mockPayRuleSetsService },
+          { provide: Store, useValue: mockStore },
+        ],
+      }).compileComponents();
+      const newFixture = TestBed.createComponent(AssignedSiteDialogComponent);
+      const c = newFixture.componentInstance;
+      c.ngOnInit();
+      return c;
+    }
+
+    it('should expose the useOneMinuteIntervals form control', () => {
+      const c = setupWithData({});
+      expect(c.assignedSiteForm.get('useOneMinuteIntervals')).not.toBeNull();
+    });
+
+    it('should default useOneMinuteIntervals form value to data value (false by default)', () => {
+      const cFalse = setupWithData({});
+      expect(cFalse.assignedSiteForm.get('useOneMinuteIntervals')?.value).toBe(false);
+
+      const cTrue = setupWithData({ useOneMinuteIntervals: true } as any);
+      expect(cTrue.assignedSiteForm.get('useOneMinuteIntervals')?.value).toBe(true);
+    });
+
+    it('should expose first-user state via selectCurrentUserIsFirstUser$', () => {
+      // The new section is gated by !data.resigned && (selectCurrentUserIsFirstUser$ | async);
+      // assert the observable wiring instead of rendering the DOM (see top-of-block rationale).
+      const c = setupWithData({});
+      expect(c.selectCurrentUserIsFirstUser$).toBeDefined();
+      let isFirstUser = false;
+      c.selectCurrentUserIsFirstUser$.subscribe((v: boolean) => (isFirstUser = v));
+      // mockStore.select returns of(true) for every selector; verifies the gate flows through.
+      expect(isFirstUser).toBe(true);
+    });
+  });
 });
diff --git a/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.ts b/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.ts
index 74ce7776d..cf6ada872 100644
--- a/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.ts
+++ b/eform-client/src/app/plugins/modules/time-planning-pn/components/plannings/time-planning-actions/assigned-site/assigned-site-dialog.component.ts
@@ -166,6 +166,7 @@ export class AssignedSiteDialogComponent implements DoCheck, OnInit {
     this.assignedSiteForm = this.fb.group({
       useGoogleSheetAsDefault: new FormControl(this.data.useGoogleSheetAsDefault),
       useOnlyPlanHours: new FormControl(this.data.useOnlyPlanHours),
+      useOneMinuteIntervals: new FormControl(this.data.useOneMinuteIntervals ?? false),
       autoBreakCalculationActive: new FormControl(this.data.autoBreakCalculationActive),
       allowPersonalTimeRegistration: new FormControl(this.data.allowPersonalTimeRegistration),
       allowEditOfRegistrations: new FormControl(this.data.allowEditOfRegistrations),
diff --git a/eform-client/src/app/plugins/modules/time-planning-pn/i18n/da.ts b/eform-client/src/app/plugins/modules/time-planning-pn/i18n/da.ts
index d2cba95c9..65556ab5a 100644
--- a/eform-client/src/app/plugins/modules/time-planning-pn/i18n/da.ts
+++ b/eform-client/src/app/plugins/modules/time-planning-pn/i18n/da.ts
@@ -311,6 +311,9 @@ export const da = {
   'Mobile registration': 'Mobilregistrering',
   Shifts: 'Vagter',
   'Payroll rules': 'Lønregler',
+  'Advanced settings': 'Avancerede indstillinger',
+  'Use 1-minute intervals': 'Brug 1-minutters intervaller',
+  'Enable 1-minute granularity for time entry. Default increments are 5 or 15 minutes.': 'Aktiver 1-minutters granularitet for tidsregistrering. Standardintervaller er 5 eller 15 minutter.',
   'How working time is captured': 'Sådan registreres arbejdstiden',
   'Manual entry': 'Manuel indtastning',
   'Allow entry of forgotten days': 'Tillad indtastning af glemte dage',
diff --git a/eform-client/src/app/plugins/modules/time-planning-pn/i18n/enUS.ts b/eform-client/src/app/plugins/modules/time-planning-pn/i18n/enUS.ts
index d53cccc23..a22cfe4ab 100644
--- a/eform-client/src/app/plugins/modules/time-planning-pn/i18n/enUS.ts
+++ b/eform-client/src/app/plugins/modules/time-planning-pn/i18n/enUS.ts
@@ -311,6 +311,9 @@ export const enUS = {
   'Mobile registration': 'Mobile registration',
   'Shifts': 'Shifts',
   'Payroll rules': 'Payroll rules',
+  'Advanced settings': 'Advanced settings',
+  'Use 1-minute intervals': 'Use 1-minute intervals',
+  'Enable 1-minute granularity for time entry. Default increments are 5 or 15 minutes.': 'Enable 1-minute granularity for time entry. Default increments are 5 or 15 minutes.',
   'Hide employee from daily operations. Requires a resignation date. All settings below are hidden.': 'Hide employee from daily operations. Requires a resignation date. All settings below are hidden.',
   'Breaks are calculated automatically from the rule set. Manual break entry on shift tabs is disabled.': 'Breaks are calculated automatically from the rule set. Manual break entry on shift tabs is disabled.',
   'Main switch. When active, select registration method and editing policy below.': 'Main switch. When active, select registration method and editing policy below.',