If you take the bus - it all depends when you catch the bus - buses usually pass through POFQ every 15-20 minutes, so if you get to the bus stop and your bus just left, you might have to wait - then it has to stop at POR, and once you get to the park, you have to get through security and ticketing, and walk from the front of the park all the way to the near the back. I would be at the bus stop at least 50 minutes before your reservation - which would be 7:45 AM.
If you have a car, then I would say be in your car 30 minutes before your ADR - 8:05 AM.
SkierPete