Originally Posted by Kiwi Flyer

Depends on the upgrade method and status.

Using airbucks you can get confirmable upgrades (subject to availability) at the time of request. These cost a lot.

Using airbucks you can also request standby upgrades. These may or may not confirm immediately, after some time, or never.

Using status evouchers upgrades are standby, and processed by status. Gold Elite up to 12 months (so can confirm immediately but won't necessarily do so), Gold shorter period and Silver shorter again. These seem to have higher priority than airbucks standby upgrades, which makes sense given the evouchers expire.

Using *A miles upgrades are standby only. I don't know but suspect these have lowest priority of the lot.