So this is an old question that I obviously missed. Hopefully you got good answers other than what I see here, because I am not sure they completely understood your question. I do.
My guess is the buyers would be happy to allow a rent back, especially if it reduces their purchase price or if you're paying rent. Yes, it's usually a couple of months before they can tear down. Their financing is not going to be for an owner occupied unit -it will be cash or construction - so that shouldn't come into play. It's just a matter of the seller being OK with it, but if they are going to tear it down... eh, shouldn't be an issue.
Have you sold your property? I work with builders in that area... if you're still the owner and want to sell, call me - 703-669-3142