Originally Posted by remyontheroad

This is not universally true.
I routinely get short checked bags, on <24hr stops, as long as there is an overnight.
Changing from a layover to a stopover (less than 24 hours to more than 24hours) will most likely significantly raise your fare, though, in addition to any change fee.

(I've even gotten them on long same day (8+hour) stops, but that's probably been a favor for a frequent flyer.)