I'm sure there are others on the board who are much more informed than I am. I can only speak from experience. We were at the Caribbean Beach Resort this past July (busy time of year). Due to the size of our resort, there were 5 stops. Busses came very often, and the most we ever had to wait was 10 minutes for a bus to the park that we wanted (other busses came to our stop, but were going to other parks). The longest part of our bus ride was always circling CBR. Once the busses left our resort, it was a straight shot to the parks, and we were never on a bus for more than 15 minutes (once leaving the resort). By staying at the All-Stars, which only have one bus stop location, each, you won't have to deal with the 5 stops that we had to. That will make your bus trip 15 minutes shorter than ours was.
We had a character breakfast at the Magic Kingdom at 9:15 am one moring, and I was worried that we would be late and miss our seating (as this was a very difficult reservation to get). We left our room at 8:00 am to walk to the bus stop. I won't bore you with the details of the trip, but when we walked-up to Cindy's castle, I looked at my watch. It was 8:30 am, and we were WAY early for our breakfast. This was in July, one of the crowded times of year, and we were traveling to the MK which is the farthest park from our resort. We made it from our room to the steps of the castle in 30 minutes. For others who have been there, they'll appreciate how quick that was for a July morning!
If you feel that you must be at a park at a certain time, I would say that going to your bus stop 30 minutes prior to that time would be more than enough. And again, you can't beat the fact that the busses take you right to the front door (well, as close as you can get) of each park. Remember, this is a "perk" only for guests staying on Disney property. That means that very many of the guests at the park will not be able to ride the bus.
If you still feel that you must drive your own car, I would leave 1 hour before you want to get there (90 minutes if you are going to the MK because even if you drive, you still have to take a boat or the monorail from the parking area, through Ticket & Transportation Center, and then get to the gate). There's no direct way to drive to the MK. Only the busses go directly to the MK.
Hope that helps... and I hope people with more information respond to give you a better answer to your questions.