The enhanced 12 Hour window is a major improvement for me.

The previous 3 hour window for confirmed stand by was far too restrictive to be helpful. If I wanted to confirm on the later flight, I would have to have missed my booked flight, and cross my fingers that at the 3 hour mark a seat would still be available on the later flight.

Now that I can get a confirmed seat in advance for a discount, I'll likely use this feature regularly.