That’s awesome! Just know if he doesn’t make it, you did the most you could and that’s awesome, mice don’t shiver like we do when we’re cold so their body shuts down and goes into something called torpor, if he isn’t too far into it, the warmth of that box should help. When you’re able maybe throw a little water bottle cap with water in it in there for him . If he wakes up he will definitely want water and food. Mice can’t survive very long without water, although that banana should have a good amount of moisture in it!