Originally Posted by samm

This isn't formally allowed, the rule is "same calendar day". Back in January I flew CUN-CLT-CHS, and had an overnight layover in CLT. I arrived to CLT in the morning and asked if I could get on one of the several flights to CHS and they were really strict and said there was absolutely no way. I expected them to say that, but had to get a hotel in CLT.

The "24 hours" you might be thinking of is when you can make the initial request to standby, just like you can check-in 24 hours before the flight.