You would not have to leave at 9. You can stay for the whole show
If the show is 16+ there will be a divider in the room that separates the people of age with alcoholic drinks and those who are under age. However, your guardian can stand in the underage section as long as they dont have a drink in hand. 21+ people get wristbands I think and unders get "x" on their hands. I think that's how you're allowed to be in there for the whole thing. You can always ask in the Facebook event discussion tab if theres an event page for it! Crescent can answer in there as well.
I am not sure about yhat answer i would call them direction
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