How do they keep track of who's time is up, are you assigned one trampoline or do they run freely?

There is a bracelet system and they call the color when time is up. Also it's a free for all

They call all people with bands of a certain color to leave

For when you have to leave they give you a different colored bracelet, then they call the bracelet color, and you leave

Color coded bracelet for each hour. They give you a specific coloured bracelet to wear when you're jumping.

Run free color coded bracelets

You have a certain color bracelet and when your time is up that color bracelet gets called