For an 8:30 am BOG reservation, I would plan to be at the gates for entry by 7:30 am as they usually let guests with pre-park opening (PPO) reservations in around 7:45 am. It will give you time to stroll down a less crowded Main Street on your way to your reservation. From reviews I have seen, they usually will go ahead and let guests in to dine before their reserved time for PPO reservations.