Not exactly usual for that age group. When I was 18-21 I attended more post-midnight parties than I can remember.
"I'm guessing no one is going to miss the party guests that got shot."
I strongly suspect your guess is wrong.
usual = unusual.
I would imagine that was especially true the night of Homecoming, the Prom, and graduation. Even stick in the mud El Gato (Then, not now) was up until well after dawn on graduation. Had breakfast at the same friend's house where we had the "welcome the exchange students" party at the beginning of the school year. That's where I met the Swedish exchange student, and asked her to the state fair. We had a good time, but even though she wasn't quite the Swedish Bikini Team type, that you DoM might imagine, she was nice and she was very smart, but somehow just wasn't my type. (My wife is German-Danish-Italian, and more blonde than the Swede, and just as smart too, at least she has a higher measured IQ than I do, and scored just bit higher on her GREs than I did.)