Are you planning on arriving at the parks 15-30 mins prior to opening? If so, you will have a lot of company. IF you want to be at a park 20 mins prior to opening, you should be out at the bus stop no less than 45 mins before opening. So, if the park opens at 8 (for EMH) you need to be at the bus stop by 7:15, latest. 7 would be even better. If you just miss a bus, it could be 20-25 mins before another one comes along.
From AoA to Epcot takes about 10 mins, to DHS, about 15.