will it freeze if i leave it overnight with no antifreeze or water

If you had antifreeze in there before you started your repair, your motor will be fine. The antifreeze ISN'T so the ENGINE doesn't freeze, it's just "winter-grade" coolant.

Basically, during normal operation, the engine makes way too much heat for it's own good. Modern car engines are designed to be "water-cooled," but the problem in cold climates is that the water (not the engine) will freeze when the engine isn't running. We've been adding chemicals to water to keep it from freezing, so we've been calling the mix "antifreeze."

If water is what you've have in there before your repair, there's always some left behind after you drain it, so whatever is left will freeze. But like I said before, if it was coolant, the left over coolant won't freeze.

With no antifreeze or water, there is nothing to freeze so it will be fine to leave it drained of all coolant overnight.