Hard to say how long for sure depending on the environmental conditions. As soon as an animal is deceased, epidermal break-down begins almost immediately. The best way to tell if your cape is bad or not is as Booner mentioned. Very lightly pull on the hair in all areas of the cape. If just a hair or two comes out, that's normal. If it comes out in clumps, he gone. That being said, it doesn't mean that it might not start slipping by the time the taxi is able to get done splitting and salting the cape or it is put into an acid pickle to be ready for fleshing. I would say in the early season, if you cant find one by the next morning and get it caped and to the taxi by the next evening, you might have to get a new cape. As long as the weather is around freezing, you might have a couple days. If the weather is below freezing when shot and your deer is frozen when you found it. It will probably be fine for quite some time as long as his innards cooled down fast enough.