Correct. Existing process says if they don't clear one day before, you're out of luck.

We don't have any real detail yet on how the day of departure upgrades will work, re:

"This means if a First or Business Class seat is available on your Delta flight on the day of departure you will be able to request the upgrade."

If that means any available seat, it may be an improvement, but most of us don't book an upgradeable fare unless we can confirm availability at the same time anyway.