The first bus usually leaves the airport at around 10:00am, and the buses run pretty much continually after that, leaving as they fill up (or if there's a lull between arriving passengers). The port terminal opens at around 10:30. Boarding usually begins at around noon, often earlier. The latest I've seen boarding begin was at around 1:30pm, but like V-Man, I've gone on at 11:45, too.