Upgrade question

Somewhat new to upgrades...have a question regarding the procedure...

Flying CVG-DEN, Friday 5/17.

I'm silver medallion.

I've kept an eye on the seat map over the last week...

Have seen number of open first class seats drop, as I assume these are being filled by Diamond/Platinum/Gold medallion 5 to 3 days out...

But, now...we're within 20 hours of takeoff, and it still shows 2 open seats in FC, but I have not been upgraded.

Just trying to understand whats going on...

I figure these are being held for last minute FC purchases?

Any idea what my upgrade chances are if I saw 2 open seats as of 9:30AM eastern time Thursday, and my flight leaves 9AM eastern Friday?

If anybody can help explain, would be appreciated.

Thanks!