You'll never wait 20 minutes for a bus INSIDE the campground. The 20 minute wait is for the buses at the outpost that take you to attractions. The busses inside the campgrounds (yellow, purple, orange) run on constant loops. We were there the last two weeks of July and I would be surprised if you ever wait as as much as 10 minutes.
My suggestion is don't be afraid to take off walking for the view and the exercise, but if you get tired, there is a bus stop every couple hundred yards on any main road. The sidewalks are great and this is one campground that actually has scenery. There is attractive plant life and we saw lots of small critters, rabbits, birds, squirrels, etc. while there. Plus it's always interesting, as an rv-er, to check out other folks rigs.