If you use miles to upgrade it is possible to get the upgrade confirmed now, or at the time of reservation, along with your seat assignments and not wait until the 100-72-24 hour sticker upgrade window prior to departure. Mileage upgrades pull from A booking code inventory and stickers pull from X inventory which does not become available until close to departure as noted above. A inventory is capacity controlled so it may be available now, maybe not. But it could possibly be changing all the time as people make or change or cancel reservations and as time gets closer to departure.