There are no busses from WL to MK. You'll have to take the boat or monorail to TTC then bus.
When we were at MK at closing during our Sept trip, mobs of people were leaving. It took abt 30 minutes "door to door" via the boat. The boat dock waiting area was packed w/ people & there was a line outside. But it did move pretty fast as lots of boats were coming & going. The monorail, on the other hand, had lines all the way down the long ramps to the bottom.