I hope he has a great time.
But yeah, I agree that the time seems a bit too late for kids that age, in my opinion.
Our local school (primary - grades K through to 6) has "school socials" on one afternoon/evening, usually the last one of the term. So on the Friday the kids get home from school at about 3.30 pm and begin getting ready. They are timed to happen in sequence. The first one usually begins at 4 pm and goes until 5.30 pm. This is for K-2. Then at 6 pm the next group assembles - grades 3-4. They go until 7.30 pm. Then grades 5-6 gather from 8-9.30 pm. These are well attended by teachers who keep everything organised. Sometimes there's a costume theme, sometimes the kids just dress up. Parents "bring a plate" to contribute to supper, for which the kids file in, walk around the bench a couple of times and eat as they walk around. I was never greatly impressed by the whole way it was done, but the kids seemed to accept it.
I do wonder if, in this case, the late start is because a younger group of kids had the earlier time slot. In which case - do the senior high school kids follow, beginning at 11 pm? I surely hope not!
Marg