No, they don't follow the normal rules, they can be in that state for weeks, even years. Personally, I've had a few I'd been watching (namely a vendor house with some old stuff I wanted) go down in the middle of a decay cycle. Needless to say I was a little miffed.
Also, I believe it was stated in the FoF, but they are working to remove OSI owned houses, and their removal won't follow the normal IDOC decay cycle.