Hi Cinch!
Years ago when my dad worked for United Airlines (he's retired now), the airline had a 1 day fare from Denver to Las Vegas. You showed up at the gate at pre-dawn with no luggage and for $25 they piled you into a empty seat. You had to come back on the late night "red eye" flight (same day)... unless that flight was full and then you headed back to the strip until the first flight in the morning. If you missed your "assigned" return flight, you had to pay full fare to get back home. You should have seen all the little old ladies in jogging suits with fanny packs hoping for empty seats back then at 4 am in Denver! Sadly, United did away with that deal years ago, but it can't hurt to call the airline reservation number and ask a senior representative.