We went last October, but stayed in the campsite in the town a few miles north. The reception sold entrance tickets including bus transfers to/from the campsite.
The park estimates for the time taken to walk the various paths are VERY conservative. Having said that busloads of Japanese tourists going in the opposite direction made walking the paths a bit of a chore. But don't let that put you off. The park is fantastic.
We were driving and visited last year, because we were staying in an onsite hotel we could buy our ticket the night before and were able to be in as soon as the park opened.
We were blessed with the most wonderful weather, walked all day and then had the benefit of the most glorious thunderstorm together with massive lightning flashes visible from our room and over the park.