I want to say it was 11 PM when we were there in June. Honestly, the bus is faster. The boat is a lot nicer, but unless you are located near the boat dock in OKW, the bus is faster. The boats run on the same schedule as the bus (every 20 min or so) but the buses get there faster than the boat, especially if you have to get from your room to the boat dock in OKW.
-dave