Prior to ticketing...If you don't cancel it, it will cancel itself after 24 hrs (or 72 for international?). Therefore, the "priviledge" you are really enjoying in that situation is not your ability to cancel, but that the airline is holding the reservation in the first place.

AA says that prices are not guaranteed, especially on non-AA sectors, until you actually buy the ticket, but in my limited experience they have always been honored till the very end.