Only by reading the tournament descriptions before you enter, which all quite clearly state how many games you would be playing.
I looked at half a dozen upcoming tournaments. The number of simultaneous games varied wildly from 1 game at a time to 22 games at a time.
I made my first tournament the other day but it looks like you cannot change how many games are concurrent overall.
What I mean is for example is someone has a 12 person tournament, all 11 games start at the same time, is there a way to limit that so you are not overloaded?