At T-21 hours, there were still 2 rev seats available for sale but they wouldn't release the upgrade to me. I called again at T-12 hours and suddenly the flight was sold out.
I have to say, given how hard I have worked to try to get this upgrade only to be told that I couldn't have it less than 24 hours before the flight, really makes me wonder why it's worth it to even be loyal to US. My understanding is that at least on AA it's easier to use the upgrades. They may have earned some incremental revenue from a few last minute pax, but probably lost the loyalty of a customer and his family of 4 who only bought these tickets on US because of the upgrade potential instead of flying LX or LH which are both nicer in coach and had cheaper tickets.