It really depends on the outside temps. It is most important to cool the deer down as fast as possible, by proping open the belly and I usually put a fan on it. It will only cool from the inside out as the hide is extremely insulant. Overnight should not be a problem this time of year unless it was hanging all day. Post back with some specifics including when it was shot, how soon after it was gutted, what has been done since, and temps. in your area. You will get a more precise answer soon.