RPGMemes

That and the changing every in-game hour. I'm rarely tracking time down to the hour, so it would either slow things down if they try to make any kind of scene out of it, or we're just going to gloss over multiple changes, potentially making the whole thing moot. Then you get into a dungeon and someone might be locked out of "their" character for a large chunk of playtime.

Tracking who controlled for longer to determine the next level up sounds pretty tedious too, but I guess that would be the players' problem to sort out, not the DM's. I would worry that it may be an unforeseen detriment to their enjoyment though.