How late would you let a boy stay at your daughters birthday/sleepover party?

My daughter turned 14 and is having her birthday party tomorrow. It's also gonna be a sleepover. She doesn't have many friends so her female cousins are coming. She has a friend who's a boy who's 15. I've talked about them on here but he moved in with her neighbors and because his dad abused him and his mom and killed his mom in front of him. He's my neighbors nephew and wouldn't speak to anyone. Even his therapist. The only person he spoke was my daughter when she went over there to talk to him. They talked about Harry Potter and the neighbor asked me if they could hang out since she was able to get him to talk and they have been best friends every since. My husband was at first absolutely horrible about it because he said boys that age only want one thing and he was just being horrible until recently I told him "Do you seriously think acting this way would change anything if he was after our daughter for one thing? Or would being the male role model that boy so desperately needs in his life have much better effects?" Since then he's let up A LOT and even apologized to our daughter. But anyway my daughter is turning 14 and he's coming to the party. She's having a sleepover and obviously it's inappropriate for a boy to spend the night at a girls sleepover. He's invited for all the fun stuff and cake and all that fun stuff. But about how late would you say is appropriate for him to stay? I was thinking maybe until the girls were ready for bed but you know how late girls stay up at a sleepover