Time preferences: ISO 8601 format

Release notes

In addition to the preferred date and time display of "exact" and "relative", users can now also set ISO 8601 / RFC 3339 in their profile.

Problem to solve

Following https://xkcd.com/1179/, I'd like to configure GitLab to display all timestamps in the ISO 8601.

That's also what the GitLab handbook recommends.

Proposal

Make it possible to tick a checkbox "Use ISO 8601 format everywhere" in time preferences.

Or, add ISO 8601 as a 3rd option, converting the current user[time_display_relative] checkbox into a list of radio buttons:

Before	After

The default/"System" options then might need a clearer name.

Intended users

Anyone who prefers this date format over GitLab's current display options. Locally for example, Git itself can be used that way:

TIME_STYLE=long-iso ls -l
git log --date=iso

One practical usage example would be to:

1. load an epics/issues/MRs list with &author_username=…&first_page_size=100
2. count with a simple created 2025-… in the browser's Ctrl+F function how many items one created in a year and/or month.

Feature Usage Metrics

If we measure the current time_display_relative state, I presume the suggested 3rd option can be added.

Does this feature require an audit event?

No, as it's a simple, user-specific display preference.