They open the Main Street/hub area to ALL park goers around 7:45am. The days of using a PPO ADR for pictures in a mostly empty Main Street or castle are nearly gone.
For those with a PPO BoG reservation, you will check in to the left of the castle and be allowed to make your way to the restaurant beginning at 7:45/7:50-ish. Don't worry about getting lost, there will be folks to direct you to the restaurant and make sure you don't wander off the beaten path. You may be allowed to ride either Peter Pan or 7DMT (although the ages of your children may prevent this one) before the rope drop crowds get there...but that also depends on whether your ADR falls on a day with Extra Morning Magic.
For your CP reservation, you'll just be there with the masses in the MS/hub area, and you can just walk up to the restaurant. There is zero PPO advantage to this reservation (other than getting breakfast out of the way before park opening), since you're still behind the ropes. Of course, rope drop may happen while you're dining at CP, especially if you're committed to seeing all the characters.