Note that for rebooking, you can be given confirmed seat for one flight and standby for an earlier one. You can ask for standby in Main Cabin (Y) with a later confirmed ticket in F if you don't mind that and just want to get to your destination ASAP. This can result in queueing up for a couple of flights before you get on one, but it can also get you out a lot faster than your confirmed ticket on the last flight next day, for example.