You should only be able to control one player in this game, so you can be batting, bowling or fielding (you're not always the one bowling). Therefore, if you want to have a bowl, you have to wait until the bowler has bowled about 10 or 11 balls, and say "Two more!" to the bowler to make him finish his over after bowling two more balls and the classic "Just one more, I'll get him out" ball.
If you time the "Two more!" call badly, and say it when the bowler has only had about 8 balls, you will get a very shortened over, as the bowler will be counting every single ball and making sure that you end your over after 6 balls. If you say it too late, then the bowler will just keep going and not tell anyone.