Leaving it overnight shouldn't cause any problems. With some, it's the only way they'll eat.

Can someone tell my why they can't digest cooked meat? Much of the nutrition may be destroyed, but I still see no reason why they wouldn't be able to break it down.

I don't know why people advocate Carbon Dioxide poisoning, as it's basically depriving them of oxygen, which in my experience is very painful. Quickly destroy the brain.