Do you care if your leftovers sit out?
Do you care if your leftovers sit out for a while before getting into the fridge?
How long is too long? A few hours? Overnight?
For example, I went out to eat with the fiance for lunch, and it was probably a good three hours before we got to the nearest fridge with our leftovers. Didn't phase us a bit, but I've heard people say you shouldn't wait more than two hours.
Heck, I've gone with overnight more than once. WAAAAY more than once.
In general, what's your threshold for leaving out the leftovers?