I may have a basic misunderstanding of how the mileage upgrades work.

I was under the impression that one could "pay" for an upgrade with miles at any time. If there's upgrade inventory available you get it. No waiting around for the 72 hour window, etc.

In fact I have done exactly this as recently as October (bought super cheapo ticket ORD-HNL and upgraded immediately after purchase with miles. Travel was at least three weeks away at that point).

This is a basic difference between upgrading with 500 milers and with miles.

Am I missing something?

For the record I am Prem Executive.

Mike