For the chat box and in-game chat, I think it would be really nice to have a little clock (just a digital readout like 10:30) beside the posts that people make. It would be relatively small, and under options you would be able to change the time zone so that it correctly reflects what time it is where you are playing from. Even though you might be able to check elsewhere nearby, you could still look at the time on the posts (whether it updates automatically on the chat box or just beside a new message.
It could be useful for a number of other things, including timing how long your games last (if you send a message at the beginning of the match) and for times when you are sitting in lobby and switch to another tab to look at something, then come back to find out that someone has been trying to talk to you (so you know if you should send a response back if it was a minute ago, or whether they posted thirty minutes ago and it's not worth sending anything back because they aren't there).
Nothing that would bother anyone, but a good add-on to the game.