It can be done. Everyone with a PPO ADR is let into the park at the same time. (You fill find a line and CMs checking reservations.) You can check in right away .....you won't have to wait until your ADR time to be assigned a table, but they may prioritize folks with a time earlier than yours.
I had a PPO on the later side and used
www.touringplans.com reservation finder to snag an earlier one....my personality made me keep trying to pull it earlier just In case
In April our server asked if we were hoping to "walk on" Soarin' .....when we said yes she said she would take care of our bill asap so we could get up whenever we were ready. We never felt like we were rushing. I enjoyed several cups of coffee, filled up (loved the huge bowl of fresh fruit) and had lengthy interactions with each character......then walked right on Soarin'. It was a great start to the day!