It is best to figure on at least an hour to get from one place to another.
You could miss the first bus just as you are walking up and the next bus might not be there for another 15 - 20 minutes. They wait a few minutes to load it up and then head back to the resort.
We stayed at SSR and there are four stops; we were the last stop at Springs, which also included the transfer stop for THV people, so it was always somewhat crowded at the stop to get off the bus.