When arriving early I usually find the first hour the best part of day 1.
Check in with no line and be on the ship when it's still empty. I've never had a line at 10:30 of more than 20-30 people and they usually have at least 10 check in agents at the start. When I did b2b(along with a total of 7 other cruisers) in February we walked off, went through customs, and had an hour before new guests came on board. Me and 2 staff where the only people on the 2 upper decks.
I got a few strange looks from staff, like aren't you supposed to be off the ship by now? lol