Thanks much for your post, RunningBun, because you made me look!
It's a month before our flight to Europe, but this evening I decided to look at what they were offering for first/business class upgrade. When I originally booked I think they were offering (the quickie special offer right after you confirm) $3000-$4000 per person to upgrade. Too rich for me!
But now they offered ~$950 per person for each direction, or $1782 for upgrading both. So we bought the outbound direction upgrade which includes business class for the overnight leg (a 2-2-2 configuration with lie flat seats). We've never flown overnight international business class before.
The reservation blew up online with some scary errors yet my credit card was charged, and I had to call in to United Reservations to get it fixed. So it seemed pretty dicey for a while and I thought I had stumbled onto some system bug that offered me something they shouldn't, but they got it all squared away after several long phone waits.
I didn't want to wait until T-24 to check because of seat availability in Polaris business class. I know from past experience that on the international flights that business class seats are in high demand, and people with high status start clearing their requested upgrades at T-7 days. Meanwhile a lot of folks are on wait lists to upgrade with miles - something that also starts to clear several days ahead depending on status. Buy the way, to upgrade with miles for still costs $550 for each direction in addition to the miles, and then you go on a wait list, and only get upgraded if someone else doesn't outrank you in terms of status. So essentially we paid an extra $400 each to pay outright and get an immediate upgrade instead of using miles.