The boats were running sooner than 1/2 hour before park opening when we stayed there at the end of September. There isn't any way to know what time the boats start running as far as I know.
You should be able to see the bus times on the
MDE app. It will tell you what time the bus is supposed to arrive at WL and what time the bus is estimated to arrive at the parks. You can use this in reverse when you are at the park, waiting for the return bus. By looking at what time the bus is scheduled to arrive at the park, you will get a general idea of when the next bus is coming. Of course, this only works when the bus times are showing.