The buses tend to get to the ship about Noon, by the earliest, or later. This is because they don't start picking up from the resorts untnil about 10:30a.m. to 11:00a.m.
Also, it seems when the buses arrive at the port from the resorts there is usually quite a line into the terminal and quite a number of folks already there. Unless you arrive later, say after 1:30p.m., in which case there may be a line through security into the terminal, but you'll walk right on to the ship in most cases.
Taking the bus from the resort to the port is great. As long as you don't want to get there early and be one of the first groups boarding. In which case you should get there around when the terminal opens at about 10:30a.m. At least this is how it used to be as of last September.
