Of course, I had nights in my college years when I was up until 3-4 AM, especially on a weekend, but I think it's very possible they were asleep when murdered, which could explain the neighbors not hearing screams or anything like that. Also, since a gun was not used, IMO it would be tough to murder 4 alert, alive young adults with a sharp object. Once one was stabbed, I would think at least one of them would be able to turn and run and get out of there. I understand flight, fight, freeze, but I would think at least one would not freeze and would be able to escape. Just my opinion of course. And if the upper floors were particularly bloody, that would lead me to believe the bedrooms may have been the crime scenes.
Absolutely horrifying. My goodness. Those young lives cut way too short.