As a follow-up to my previous post, I flew NYC-LAX New Years Eve.
I originally booked tickets in economy for a 9pm flight about a month beforehand and requested an upgrade for my wife and I during booking. As a reminder, I'm PLT so the upgrades for two passengers would require 10 stickers.
At the time of booking, and all the way to the day of the flight, AA's site showed the J cabin being completely open except for two seats. The upgrade didn't clear in advance, and my wife and I were placed #1 and #2 on the waitlist (which had a total of three people on it, including us).
We arrived at the airport around 5:30pm, and I explained to the TA that our top priority would be sitting together in J, and the 2nd priority would be moving to an earlier flight. She explained the following cabin loads:
7pm flight: 6 seats in J were available with 4 people on the waitlist. My wife and I could standby for it, but would become #5 and #6 on the upgrade waitlist due to our unconfirmed status on the flight.
8pm flight: The J cabin was almost 100% open, and only 1-2 people on waitlist. Again, my wife and I would be at the end of the upgrade waitlist due to standby status (moot).
9pm flight: The J cabin was almost 100% open, and we were already #1 and #2 on the upgrade waitlist.
As the 7pm flight boarded, I explained to the GA that we were on standby but would only change flights after we knew we could sit in J. This overwhelmed her a bit, but a more veteran GA came in and knew exactly what to do. After they boarded everyone else on the plane, the agents printed-out two boarding passes for us in J (sitting together).
The inflight service was nothing special for the holiday. The flight had to wait a bit on the runway, but we were about 2/3rd's through the flight during midnight EST and were able to get to the hotel by midnight PST.
tl;dr Unsurprisingly, there's extremely good upgrade availability on evening flights New Years Eve.