Officially the house keys are normally handed over at closing, once there is a delivery of deed (DOD).

It can take a few days for things to be recorded with the county assessor, but that's usually not required for a buyer to take possession.

When possession should not transfer is at any point before the loan is funded and everything is signed. There is so much risk in allowing a buyer to move in early, or giving the keys over beforehand. It does happen where the closing happens but the money never comes from the lender.

Can you imagine giving the keys to your house to someone only to find out a day or two later that they can't actually buy the house? Even if you're confident in the lender and the closing just happened late in the day, do not give the keys over until it is funded. We have known Realtors to give the keys to the buyer to start moving in. What happens if there is an accident or someone gets hurt during moving... whose house/responsibility is it?