I stopped in at WHL on July 15th this year on my way north. I don't know what time it was that I got to the boatdock, but pretty darned early - I don't carry a watch, and had no idea that the boat ran on a schedule or what that schedule might be - it didn't seem to be listed next to the horn that I recall.
It was a bit of a wait, but that was fine by me. The owner seemed nice enough - I bought enough food for the next day. I was early enough that I rode back to the trail with the overnight guests so I wasn't inconvienceing anyone really. Made the wilderness only require me to carry 3 days of food, and I was glad to not have to carry a fourth.
-Jay