I received the following instructions at a recent tournament...
1) Don't wear your watch.
2) The start time is first pitch.
3) Write the official start time on the lineup card.
4) Inform both coaches of the official start time.
5) The official start time will be an announced time-of-day, not when you punch your countdown timer.
Hmmm... I'm gonna be awfully busy between signalling "PLAY" and getting into my set position!