Never timed it, but it's definitely less than 10 minutes. Problem is it's 20 minutes between ferries, so you're looking at a worst case scenario of about 30 minutes total.
In our opinion it is noticably quicker than the POR to DTD boat. Two types of boats are used, and the smaller boats are a little smaller than the POR boats, but the larger boats are substantially bigger, big enough to allow ECVs and strollers to roll right on.
There are also boats from WL that do the loop between WL, CR, and FW. These tend to be the smaller boats, but the ride to CR is very quick if you want to catch the monorail there or walk through to MK.
I love both boat rides! The POR to DTD is about 20 min, add a few more if you are stopping at POFQ to pick up passengers. So scenic.
And the ride from WL to MK is around 10 min. I think how you get there is half the fun, and so relaxing, and much more fun then the bus.