I'm trying to upgrade a flight with 500 mile certs. I just hit the magic number of hours before my flight when my Premier Executive status says I can upgrade. There are 8 seats open in First Class (SFO-HNL: UA 61), yet I got waitlisted. What's up with this? Is UA hoping to sell First Class seats between now and the date of my flight? If so, how long do they wait? Or will other flyers be offered to buy ugrades at check-in, and get priority over me? Thanks for any and all responses.