The four murdered roommates arrived home before 2 AM. The two living roommates arrived home around 1 AM and went to sleep.
Madison and Kaylee brought food home, and made 7 phone calls until almost 3 AM. They are confirmed alive at 3 AM. The murders can apparently be confirmed as having happened before 4 AM. How do police know this? No idea. Maybe one of the victims was wearing a fitbit, where increased heartbeat was detected, then heartbeat stopped ... before 4 AM?
I think this was premeditated, and that the killer knew where the target lived before that night. I think the killer spent time on the hill behind the house looking into the bedrooms.
I think that the killer and at least one of the victims had at least one prior interaction - might be something as insignificant to the victim as passing on the street. Something triggered the killer to get some fantasy in his head regarding the victim and a hunting knife ... premeditated. He might have followed the targeted victim that evening, perhaps the killer parked near frat party cars and walked around behind the house, sat on the hill, looked into the bedroom windows.
Lights went out around 3 AM. Wait 30 minutes for everyone to pass out sleep, enter through the damaged patio door.