I went to the Concierge Desk at the BoardWalk and told them that I had to be at Animal Kingdom Park at 8:15 am for a tour the next day. He said the buses start running 1 hour before the park opens. The park opened at 9:00 that day. So he said I had to take a taxi.
He didn't say anything about early buses for breakfast ADRs at the parks.
He could have been mistaken...