I've seen people waiting in line to get on the ship as we're getting off the ship at 9:00am!
__________________ Travel Agent/Cruise Specialist w/12 yrs exp and 47 Cruises on 11 cruise lines! Favorites: Paul Gauguin - Tahiti: Uniworld River Cruises - Europe; Celebrity Solstice-class ships; Holland America - 12-nights Baltics & Russia; RCCL - 14-nights Greek Isles, Turkey, & Croatia; Holland America - 14-day Alaskan cruisetour; 10-night Canada/New England cruise; 21 days Hawaii w/7-night NCL cruise; Oceania - 25 days in Asia; more than 3 months touring Europe by train. And many all-inclusive resorts!
I usually arrive at the port at between 10, and 10:30 A.M., and the porters are always at curbside, taking luggage for the afternoon sailing. The ship rarely starts boarding passengers before about 11, so there's not any real advantage to getting there much before that. You'll just get to sit in the waiting area for an extended time.