Format dates before creating timestamps

app/assets/javascripts/lib/utils/datetime_utility.js

@@ -175,6 +175,7 @@ export const localTimeAgo = ($timeagoEls, setTimeago = true) => {
   function addTimeAgoTooltip() {
     $timeagoEls.each((i, el) => {
       // Recreate with custom template
+      el.setAttribute('title', formatDate(el.dateTime));
       $(el).tooltip({
         template:
           '<div class="tooltip local-timeago" role="tooltip"><div class="arrow"></div><div class="tooltip-inner"></div></div>',

changelogs/unreleased/sarnold-format-timestamps-locally.yml

+---
+title: Fix timezones for popovers.
+merge_request: 24942
+author:
+type: fixed

spec/frontend/lib/utils/datetime_utility_spec.js

 import { __, s__ } from '~/locale';
+import $ from 'jquery';
+import '~/commons/bootstrap';
 import * as datetimeUtility from '~/lib/utils/datetime_utility';
 
 describe('Date time utils', () => {
@@ -563,3 +565,23 @@ describe('approximateDuration', () => {
     expect(datetimeUtility.approximateDuration(seconds)).toBe(approximation);
   });
 });
+
+describe('localTimeAgo', () => {
+  beforeEach(() => {
+    document.body.innerHTML = `<time title="some time" datetime="2020-02-18T22:22:32Z">1 hour ago</time>`;
+  });
+
+  it.each`
+    timeagoArg | title          | dataOriginalTitle
+    ${false}   | ${'some time'} | ${null}
+    ${true}    | ${''}          | ${'Feb 18, 2020 10:22pm GMT+0000'}
+  `('converts $seconds seconds to $approximation', ({ timeagoArg, title, dataOriginalTitle }) => {
+    const element = document.querySelector('time');
+    datetimeUtility.localTimeAgo($(element), timeagoArg);
+
+    jest.runAllTimers();
+
+    expect(element.getAttribute('data-original-title')).toBe(dataOriginalTitle);
+    expect(element.getAttribute('title')).toBe(title);
+  });
+});