Stick with your original plan:
7/19 - SFNE & Lake Compounce
7/20 - Dorney & Knoebels
7/21 - SFGADv
This is your best bet. Dorney will be dead on a Monday, so if you go there first, you'd have done everything by 1-2pm. Spend the rest of the day at Knoebels, then drive down during the night to SFGAdv.
EDIT: I overlooked that you're flying in and out of Philly. Do you have an arrival date / time yet? That would help determine if it's actually worthwhile to make the hike up to CT and MA for SFNE and Lake Compounce. I'd almost say that you should skip that trek and spend the full day of 7/19 at Hersheypark instead, like rubysparkles. Depends on how dead set you are visiting those two parks.