On average what time does an 18 and over show usually end? 2 bands 9 pm start. I'm trying to figure out whether to drive or if I'd have time to catch a 12:50 train back.

That's one of the hardest parts of Adulting, leaving shows early while all your friends are still having fun. I suggest trying to sleep at a friend's and catch a train in the morning.

Usually 12 PM. You would need to leave a little early. Depends on the bands. Some will go to 1.