It's going to vary a bit, but if you really need something specific but don't mind a bit of arbitrariness, you could pick something overly generous with the thawing time. I.e. : rat pup or smaller - thaw in water 1 hr. Finish with hot water 100F+ for 3 min. Feed rat at 95F - 105F. That way it's absolutely guaranteed to be finished every time, even if it was really finished a decent bit earlier.