You can't really know as it depends when previous games end I believe. The best you can usually hope for is to choose a game with a reasonable amount of time per player so you can get through the game, or choose one with playing hours that suits you (rather than 24 hours a day). I'm talking about turn-based tournaments here, I have no idea how anyone plays real-time tournaments unless they just hang out online all day or something (but I've never played them, so unsure).
That said, even with a reasonable amount of time per player, a bad timezone combo with the player before you can still cause problems there, since tournaments run on fixed time (that is, if it says 5 days per player, you get 5 days total to play all your moves for a single game, including time you may not be on BGA, eg. sleeping). It's up to you to decide if you want to take the risk, accept possible time penalties (which don't give you any corresponding karma penalty) and possible bootings if you have less than kind opponents. A booting will give you a karma penalty, though only a fairly small one, which is easily earned back by just playing other games and not getting time penalties/booted - the only issue is if you are unlucky enough to get a lot of bootings in a small period of time (which could happen if you signed up to a lot of tournaments that all run at the same time, but is probably fine if you're just signing up to a few). I play quite a few tournaments, regularly get time penalties, occasionally get booted, and generally run at 90-100 karma. I also play other games outside of my tournaments though.
