While making Tusker House for an 8 am breakfast is possible, it seems unlikely.
With an 11-12 m/m pace, you will probably start about 5:40 and finish about 6:50. If you walk quickly through the finish area and back to the bus stop, you might be there by 7:00. If you bus is waiting and leaves as soon as you board, you might get back to your hotel by 7:15. If you are quick when you shower and change, you might make it back to the bus stop by 7:30 and if your bus again leaves as soon as you board, you might get to Animal Kingdom by 7:45. With tickets in hand, minimal line for bag check and walking with purpose, you could be at the restaurant by 8.
In all likelihood, your bus connections won't be that smooth, you'll take more time in the finish area, and you won't be able to shower and change that quickly.
I would say 9 is very doable and 8:30 is possible but will still require you to hustle. -- Suzanne