Thanks... I followed the link to the other discussion, and found this:
Originally Posted by SanDiego1K
I flew my first UA flights with US flight numbers this week. I learned two things that were very useful.
- I was able to do online check-in on the United website the day before. I was able to enter my request for an upgrade at that time. The morning of my flight, I knew I had upgraded seats as my upgrade balance had dropped appropriately.
- When getting my new boarding pass for my outbound flight, I asked the UA agent to put me on the upgrade list for my return which was three days ahead. She was able to clear my upgrades immediately. (I am 1K.)
That's good enough for me, although I'd prefer the 500 milers to clear 48 hours in advance...