I thought I understood this but apparently I'm still confused.
I just received an email notification that my upgrade had cleared for my Friday evening, July 1, flight. I'm just FO so I thought I wouldn't clear until T-24. The email was received at about 6:15pm on Wednesday for a 6:40pm Friday departure so it's a bit over T-48. Availability is currently showing F4 P4 A0, though I didn't check it prior to receiving my upgrade as I wasn't really expecting to get one.
Luckily I'll have a nice, FC seat, in which to ponder my bewilderment...