Originally Posted by
danapop
This would be a same day standby as opposed to a confirmed change. Which is really confusing because I dont know the material difference other than one is free one is $75
SDC is confirmed. As soon as you make the change, you are fully booked on the new flight. This could be done nearly 24 hours in advance - same operational day.
With standby, you're waiting until usually quite close to boarding time to find out whether or not you can get on the earlier flight.