Is this the case in MLB? I had never heard of it so I just took a glance at the MLB rulebook and didn't see anything to that effect.
Rule 8.04. The limit is 12 seconds. It's at the umpire's discretion, and it only applies after the pitcher has the ball and the batter is in the batter's box. But the umpire can call it any time he feels there is a delay of game and award either a ball or a balk if runners are on base.