The boats run every 15 minutes or so. But I'd allow at least 45 minutes to get to your destination b/c the boat goes to Fort Wilderness as well. I know they switch the order in the afternoon, too. In the mornings I think the boat goes Fort Wilderness-WL-MK and in the afternoon it goes WL-FW-MK.
You can also take the bus to WL. That is a 4 minute ride. But again, allow at least 1/2 an hour to catch the bus. You never know if you'll show up at the bus stop and a bus will be there or if one has just left or if one is coming. I believe the busses run every 15 minutes or so, but just give yourself plenty of travel time.