diff --git a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js
index cca5635..59af36d 100644
--- a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js
+++ b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js
@@ -234,10 +234,8 @@
      * User-perceived app start time, should be reported when the app is ready.
      */
     appStarted(hidden) {
-      const startTime =
-          new Date().getTime() - this.performanceTiming.navigationStart;
       this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY,
-          TIMING.APP_STARTED, startTime);
+          TIMING.APP_STARTED, this.now());
       if (hidden) {
         this.reporter(PAGE_VISIBILITY.TYPE, PAGE_VISIBILITY.CATEGORY,
             PAGE_VISIBILITY.STARTED_HIDDEN);
diff --git a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html
index 8b85074..2087790 100644
--- a/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html
+++ b/polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html
@@ -61,11 +61,11 @@
     });
 
     test('appStarted', () => {
+      sandbox.stub(element, 'now').returns(42);
       element.appStarted(true);
       assert.isTrue(
           element.reporter.calledWithExactly(
-              'timing-report', 'UI Latency', 'App Started',
-              NOW_TIME - fakePerformance.navigationStart
+              'timing-report', 'UI Latency', 'App Started', 42
       ));
       assert.isTrue(
           element.reporter.calledWithExactly(