Nice trip report! Glad you had a good time. Did you feel you had to return the night before for an 11:30 AM ferry or was it a preference?

Some of the BBs will show as available at 6:59AM but have already been reserved the day before by folks paying the extra $550 or so for the week.
If you have the misfortune to set your eye on one of those you'll lose out no matter how fast you are. BB claims to sell only a limited number of advance bookings, but it would be a lot more transparent if they were distinguished in the interface.