Don’t think of pizza as food for your party– think of it as a party activity, especially for a not too huge slumber party. And for reasons of parental sanity retention, slumber parties should NEVER be all that big to begin with.
As the evening wears on, and they start needing something to do besides giggle and gossip, march them into the kitchen. I don’t recommend that they make their crust or their own sauce from scratch-it just takes too long. Conversely, providing them with cut bagels or cut pitas to just top and pop in the oven isn’t much of an activity.
Buy the pre-made dough (or make it yourself ahead of time) that then needs to be rolled out and shaped, and they’ll be good and busy for a while. Borrow a couple of rolling pins from the neighbors and some pizza pans from your friends. Buy the mozzarella cheese chunks and hand them a couple of graters. Let them roll and shape the dough right on your nice clean countertops without fooling around trying to do it on a dough board (using a board is just too difficult for kids- and for me). Unless you’re going to be there supervising the entire process, give them pre-sliced pepperoni so nobody loses a finger. Make your sauce ahead of time yourself or give the kids bottled sauce.
While the pizzas are cooking for their 15 minutes, hand the kids sponges and your vacuum cleaner and ask them to clean up.
I’d aim to have the pizzas ready to eat between 11 and midnight. This is early enough that your preteen or young teen guests are alert enough to accomplish the task, and probably ready for a good snack. And it’s not so late that the snack is going to keep them up any later than they would’ve stayed up anyways. Just make sure that the drinks are caffeine free.