diff --git a/.forgejo/workflows/testing.yml b/.forgejo/workflows/testing.yml
index 7a93bb66a8..4c5e18a5e9 100644
--- a/.forgejo/workflows/testing.yml
+++ b/.forgejo/workflows/testing.yml
@@ -37,7 +37,11 @@ jobs:
       - run: make deps-frontend
       - run: make lint-frontend
       - run: make checks-frontend
-      - run: make test-frontend-coverage
+      - run: |
+          # Usage of `dayjs` can be impacted by local system timezone and can be sensitive to DST differences; since
+          # frontend tests are very short they're run twice with varying DST rules to reduce regression risk.
+          TZ=Europe/Berlin make test-frontend-coverage
+          TZ=America/Edmonton make test-frontend-coverage
       - run: make frontend
       - name: Install zstd for cache saving
         # works around https://github.com/actions/cache/issues/1169, because the
diff --git a/web_src/js/webcomponents/relative-time.js b/web_src/js/webcomponents/relative-time.js
index 2ec87450c1..c070cd6795 100644
--- a/web_src/js/webcomponents/relative-time.js
+++ b/web_src/js/webcomponents/relative-time.js
@@ -1,6 +1,9 @@
 import dayjs from 'dayjs';
+import utc from 'dayjs/plugin/utc.js';
 const {pageData} = window.config;
 
+dayjs.extend(utc);
+
 export const HALF_MINUTE = 30 * 1000;
 export const ONE_MINUTE = 60 * 1000;
 export const ONE_HOUR = 60 * ONE_MINUTE;
@@ -103,8 +106,8 @@ export function DoUpdateRelativeTime(object, now) {
 
   if (!now) now = Date.now();
 
-  const nowJS = dayjs(now);
-  const thenJS = dayjs(absoluteTime);
+  const nowJS = dayjs.utc(now);
+  const thenJS = dayjs.utc(absoluteTime);
 
   object.setAttribute('data-tooltip-content', ABSOLUTE_DATETIME_FORMAT.format(thenJS.toDate()));