A nice feature for the software would be to allow people to opt-in to adding their time zone to their profile.

I prefer to see async games Move Along at a good Pace. Therefore my favorite async setting is fast async.

Knowing player's time zones would be particularly helpful when seating people in fast async tournaments. In such a tournament, if you have players from three continents dispersed around the globe, you almost guarantee time outs and very slow play.

I'm experiencing this difficulty in real time running a tournament. We have at least one player from Australia and at least one player from Europe. I only know this because I asked them where they were after noticing a number of timeouts and slow play. Fortunately, we haven't had Australia / USA / England match up yet. In that combination, there just isn't enough overlap of waking hours to allow for Rapid simultaneous play in the midst of an async game.

Here is a link that gives a visual representation of the problem:
https://www.worldtimebuddy.com/?pl=1&lid=2988507,22,7&h=2988507&hf=1

Because I understand the problem, and know which player is Australian and which player is European, I am able to avoid putting them in a matchup that includes The Americas. Should that match-up naturally occur, with the permission of the players I can switch players in order to avoid it. Obviously, this would not be possible in a final-round championship. At that point I would probably have to change the setting of the game speed to Infinity.

Anyway, having time zone information available in advance for each player would allow players to avoid such circumstances.