[feritcemkahraman]

A duration with datetime="1970-01-01T00:00:00.000Z" renders its initial value but does not schedule automatic updates. The observer treats the valid timestamp 0 as a missing date.

Schedule updates for every valid date returned by the existing getter. The regression starts at five seconds after the epoch, runs the scheduled tick, and checks that the duration becomes six seconds.

Validation: the regression did not receive a scheduled tick before the fix; all 636 Chromium tests pass afterward. Full TypeScript, ESLint, ESM/bundle and element-manifest builds pass on Node 24. Tests use the repository's Dubai time zone with an explicit English browser locale. The Windows cleanup hook was skipped and the same lint/build tools were run directly; Firefox and WebKit were not run.

[Copilot]

🟢 Approval recommended

The focused fix preserves date validation, and the regression verifies the corrected scheduling behavior.

No open issues 🎉

What changed in this PR

Fixes automatic updates for <relative-time> elements whose date is the Unix epoch.

Changes:

• Accepts timestamp 0 when scheduling updates while preserving invalid-date handling.
• Adds a regression test verifying a scheduled duration update from five to six seconds.

File	Description
test/​relative-time.js	Tests scheduled updates for the Unix epoch.
src/​relative-time-element.ts	Removes the guard that incorrectly rejects timestamp 0.

_{Review effort: Max}