You can modify and cancel up to 30 days before check in date. But if under 30 days out, points go into holding which means they must be used in the current use year and can only be used to book a vacation up to 60 days in advance. So they become distressed and you have to find something before end of use year and can't book until 2 months out or less (last minute). I use Hilton Head for this, easy to book last minute off season there. If you cancel over 30 days out, you can re-use points (they go back to how they were) and can bank them if still in banking window. This is why folks suggest buying a use year that will be at beginning of your typical travel period. For example, we typically would travel from Aug through Jan. We got Aug UY. If we book trip in Sept and cancel, we have plenty of time to still bank points if we choose not to book something else.