Originally Posted by
Kmxu
If PZ spaces (PN for GS) are available within T-24 h, phone/UC agents can certainly get the upgrade cleared. The failure rate was small for me. I could not get the upgrade cleared when the gate agent had taken over the control of upgrade process (typically, within T-1 h). So, if you see PZ spaces, you should call as quickly as possible.
I think most of us have stories of clearing into PN/R inside T-24. And most of them are at least several years old. Before UA took away the ability to apply instruments online within T-24 and instructed their agents not to do it for passengers.
Do exceptions occur? Of course. But if you're counting on (a) UA opening PN/PZ at T-1 when a flight is J1, and (b) getting an agent to clear you into it, well, good luck with that. Because the odds are very very low it's going to happen.