Maybe around 15 minutes up to 30 minutes. Depends if the boat stop at the WL first. Unless they change the pattern. They also have a bus they goes directly from the MK to the WL MHO
I would say 15min or so- maybe 20. We rarely waited for a boat. It was relaxing and very easy. We did rope drop at MK and headed back to WL for nap, pool time and usually ate at Roaring Fork before going back to MK for 1-2 hrs. We Only used the boat for MK. We also had a very easy time leaving Wishes as we got the first boat back.
The boat ride is short, it's the wait for the boat that takes the longest. It wasn't anything I would consider to be too long, though, for an afternoon break.