My DD uses the rocker start. I think her cue is when the ball is at 12:00 she takes off.
Every player I have video on who uses 12:00 trigger is late. From 12:00 to pitch release takes a little more than 0.1 seconds. It takes a little more than 0.2 seconds to take a full running stride. So a 12:00 trigger is going to be about a half step late...roughly 2-3 feet for most players. I agree with those who say rocker style is better IF (and that is a BIG IF) timing is perfect but my guess is that the advantage is less than 0.1 sec. The P drive heel raising or the stride knee forward seem to be good triggers for rocker style but the timing is not easy to master. I wouldn't spend too much team practice time on it for most players but the speedy ones who are going to be stealing often should definitely work on it often with video.