I am booked on a 6:48pm IAH-PHL flight next week. It turns out that we can leave earlier in the day than we first thought, so I'm wondering what is the best plan to try to standby on one of the earlier flights.

I am under the impression that if I call that day to check on availability of the earlier flights, they will just try to get me to pay $100 to change to an earlier flight. I am also under the impression that I would be able to change to an earlier flight free of charge (assuming seat availability, of course) at a kiosk (but not with online checkin).

I know that the simple answer here is to get to the airport early and try to standby, but we live an hour from IAH and want to avoid sitting in the airport all day if we're unable to standby on one of the earlier flights. Is there a limit to how far in advance I can checkin at a kiosk? Is it possible to use a kiosk 24 hours in before the flight?

Thanks in advance for any suggestions.