I think he was there at 0404 (in the wee hours of the morning) when he was cruising around just prior, and then executes the three point turn.
It is a very brief time indeed - and in fact, to me is so far the most surprising fact we've learned from the PCA. Who would have thought that?
Which is why I believe he went in to kill, used his boxing skills combined with big knife "skill" and rapidly bore down upon his targets. I believe he thought speedy skilling would reduce his own overall risk, as an apparent proponent of Rational Criminal Theory or whatever that's called in criminology (this is from some source posted yesterday, a student or professor mentioned it but I can't find the link so IMO he liked that theory).
Rational Choice Theory is what it's called (at least I bookmarked the proper name). The idea that explaining a crime is best done by considering that criminals are capable of reasoning and rational action, within the framework of their own goals.
I think this particular person would have a hard time actually going back into the house (which he wanted to do, IMO, when he realized the sheath was missing) in broad daylight. He would have had a hard time facing up to his bloody crimes in the light of day.
This man hoped for a relatively "clean" experience for himself and planned his murders (including where he placed the stab wounds) with that in mind and I believe we may hear more about that at the prelim or whenever the autopsies are eventually discussed. Things went to plan on the third floor, more or less, but because Xana was still up and about on the second floor, he may have been flustered. He may even have injured himself, as Xana was not in bed and his method (probably kneeling on the victim's legs or similar in order to immobilize them) was thwarted. She did not bleed out on the mattress as he had planned, there was blood all over the floor and he stepped in it.
So the latent print(s) and the visible prints, as well as the sheath were all things he did not plan to leave behind. I wonder if any DNA would have been found if not for the knife sheath. Fibers, maybe, but I bet he's disposed of every item he wore that night, along with the knife - probably that very night. LE may have some idea of how many times he stopped (some of his stops seem to be documented in the PCA).