I would take the 8:20am ADR.
. . . arrive at park the gate for 7:45am entry *
. . . go to Tusker and start breakfast
. . . you can be seated almost immediately when the eatery opens
. . . ask waitress for the check WHEN you sit down
. . . it can be paid while you eat
. . . you will be out in time for the park opening at 9:00am
Even if you aren't out exactly at 9, you'll still be out early enough to reap the benefits of RD.
Kind of going back and forth on ADR time for TH breakfast. Option 1 - go at 820 and be done shorty after park opens. Option 2 - do a few attractions and then have breakfast at 1030. What would you do ?