Some thoughts after reading the PCA again. I'm really curious what time precisely that DM awoke the first time. It says approx 4 and she was awoken by what she thought was K playing with her dog. We know that at 4 is when the Door Dash driver arrived, so my initial thought was that that could have woken her, but IMO that wouldn't have sounded like someone playing with a dog on the third floor. So I wonder if she woke up later than 4, possibly when BK was already in the house.
When she says a short time later she hears someone say "There's someone here," I do think that was X. The PCA also states it could have been X as data showed she was on TikTok until 4:12. IMO I think M and K were already asleep at this time. There was nothing in the PCA like data from their phones stating that they were awake. We know the phone calls to J stopped by 3. I think they had been hanging out in M's room eating their pasta, drunk dialing, scrolling their phones, etc. and sometime after 3 but before 4 fell asleep in the same bed together. They were lifelong friends and I don't find this odd at all. I also wouldn't find it odd that K's dog was in the other bedroom. Sometimes dogs like to spread out on a bed - and possibly it was used to being in that room from when K lived in the house. I recently had Covid and spent some time sleeping on my recliner in the living room because I was so stuffy I couldn't sleep laying down in bed and my dog chose to still sleep in my bed in the other room so she could sprawl out lol.
My thought is X got the Door Dash food and brought it back to her bedroom for either her and E to eat or E was asleep and she ate it alone. Just ten or so minutes later when the Door Dash guy is long gone, she hears what sounds like someone either opening the sliding door or walking through the kitchen area and says (very possibly to E), "There's someone here." Or possibly she heard someone walking up the stairs or moving around upstairs but knew the two girls upstairs were already asleep. I think he quickly killed both girls upstairs. I agree with the poster who said maybe this was a mission to rape M and he had no idea K would be in bed with her, so he therefore ended up murdering both of them as they both woke up.
He then came back downstairs and possibly X was in her doorway or outside of it checking to see who was in the house and what was going on, so he pushed her back in her room to murder her, and then subsequently discovered E. At this point would be when DM opens the door when she hears crying and the comment "It's OK. I'll help you."
The thing is we don't have definite time stamps of when DM opens her door three times. She may have glanced at a clock once to know it was after 4 but otherwise doesn't know herself. It's possible she also would open her door, lay back down, drift off, then awake again, open the door again, etc. so her timeline is fuzzy as she was unsure how long she'd drift off for between door openings. All IMO only.