You can confirm upgrades with miles at the time of request, assuming that upgrade space is available. If the space is not available, you will be waitlisted - your upgrade could then clear anytime up to departure.
Originally Posted by flyastrojets
I tried searching for this without luck. My appologies if I should've tried harder.
But I didn't see this addressed.
If I'm traveling and would like to confirm an upgrade using one of the 8 or 15K mileage awards, can I confirm that at the time of the request. Or does it have to wait and clear within the tier status upgrade window?