IMO, well worth the $100 and miles. Six hrs in Y on the 762 will suck. Also, do you have 10 stickers in your acct? If not, factor in the cost of the ones you need against that $100. However, last min, you are probably on a Y fare, so it will be free. Remember, chances are nobody has cleared the upgrade list, and you will fall behind any pax with flexible J or D fares that show up early and want to take your flights, as well as any EXPs who are on the list. Assuming that you don't just want to spend the money and miles, here are my two suggestions:

1. Call back and ask about YUP fares. If they open a few of those up, and you are already on a Y ticket, you probably won't have to spend too much more.

2. Call at exactly 4hrs, when all remaining J inventory converts to R. People here claim that works.

Otherwise, I'd start praying .