It is a long time.
So who does it bring suspicion upon?
Her family, friends, DOSS, and PF.
I rule out family and DOSS in any involvement. Obviously. We have not heard of friends in Woodland Park. I think KB was more isolated than we would like to think a successful professional woman would be. She was in cowboy country, and had a child and didn't really fit in there as far as I can tell.
It seems to be an odd situation where the texts on the 25th did what they were supposed to. This is surprising, but I think that is all there is to it- it worked. I don't believe at any point, PF thought he had more than a day or two to complete his coverup.
My point is that I don't think of 11 days as a time to coverup for a crime of murder, I think a day or two at most. PF had no way to know how much time he had.