Is there a time at which a high school can not play past on a school night? A game last night went 15 innings and was over at 1am and that seems a little extreme to me on a school night.

Sounds to me like it isn't the "length of game" that's the issue. It's the start time.

We played a doubleheader last year where we started the first game at 4:15 and the second one about 25 minutes after it finished. We went into 14 or 15 innings and were still done by 10:30PM.

A state association may adopt game ending procedures that determine how games are ended. Otherwise, play till you have a winner or the opposing coaches and UIC can come to a mutual agreement as to how to end it.