I don't know why there is only 2 extreme possible. Either 3 mins which is probably not long enough for 7 more people to come, or 30 mins, which is much longer than anybody's patience.
There should be some where in between, and best is to allow the player to adjust the time limit freely.
Another the thing is there is a need to prevent someone from accidentally joining a room from quick melee at 0:11 and stuck with a match they don't like.