You dont need to be that early in Sape. Ticket Office will officially open at 8am
But when I was there it opened at about 7:30am
Some Locals told me that you can't trust the Ferry to run every day, but there should be two Ferrys a Day (9:00 and 16:00)
(also on the Way back Labuan Bajo to Sape there are two Ferrys at the Same Time. 9:00 and 16:00)
Be sure ...