My proposal: A field in the postbit that shows the local time for a user.
Purpose: This will help users get an idea of when they might expect a response from another user (especially a mod, if it concerns warning and/or infractions).
For games with a timed phase element (such as mafia games), moves you make need to take into consideration the timezone of the other players. Knowing what time it is for them will be especially helpful.
Shiny Celebi has also pointed out that it could have some use for the traders in the trade forum. This will help them find traders within their time zones so that neither user wastes time trying to initiate a trade and finding out that they cannot do it due to radically different time differences.
Tools needed: A mod, of which there is one here.