I feel your pain, I'm on a flight Friday, JFK-NRT-HKG, back via SEA.
I booked the flight about 2 months ago and upon booking was able to secure the GUC on the return flight, which is most important to me as this is my last MR for---probably ever.
This gave me 3/3 on scoring the GUC upgrade, I have one left
I decided about a month ago to use it for this MR and was told I had to go on the wait list for JFK - NRT, but I could cash it in for NRT -HKG. I don't want to use a GUC for a 4.5 hour flight so I wait listed the longest leg and if that goes through so does the final leg. There were 20 seats open in first.
As of today there are 17 seats open and the DM desk says it will be day of clearance, due to revenue managment holding the seats for sale, they show lots of last minute purchases for this route, historically, or that's what they say.
Funny on the ride back there is only 1 other open seat showing open, but for me that GUC is already confirmed, glad rev mgmt missed calculated that flight
I'm hoping to get the clearance, but if not I have until March to burn the last one.
All part of the GUC game, I hope you get to use yours before they expire!