The ART Bus schedules coincide with the hours in the park. I have used them for regular park opening, and for early entry as well. They have never let me down. I usually stay at Dolphin's Cove, and catch the bus that stops in front of the Travelodge on Harbor, near Orangewood. If the park opens at 8 a.m, I always try and be at the bus stop by 7. That works quite well.
I also buy my ART passes online. They will mail them to you, and only charge a very small shipping charge. Since I am over 65, they even gave me a discount. When they send the passes, they also send you one of their brochures. It lists all the routes, and is very informative.
I have used the ART for all the years that I have been visiting Disneyland. One exception was my stay at the Candy Cane Inn. They have their own free bus.