How long can hermit crabs go without heat?

they don't hibernate. they do tunnel down into the sand to molt (shed their exoskelaton and grow). the length of molting depends on the size of the crab. tiny ones can take two weeks, meduim (Golf ball sized) can take from two weeks to a month or two, really big ones can even take 3 months. never disturb a crab while it is molting.