I agree with not leaving rats or mice in overnight - especially with no food or water available to them. But a rat or mouse isn't going to just randomly decide "oh - I think I'll go gnaw on you for a bit", it's just not how they behave, especially a well fed, well hydrated rodent.
The longest that I personally leave prey in with my animals is 30 minutes, any longer than that, I feel that the snake is more stressed by the prey's presence than not.