They will usually start processing passengers around 11am. You do not want to get to the pier too early since they are still getting the previous guests out of the way.
Show up around 11am and you should be aboard sometime after noon if not earlier. Go to the Windjammer and get lunch. It will already be open. You will not be allowed in your cabin until 1:30pm at the earliest so you'll have to schlep your carry on bags around with you. Eat, get out of the way for someone else to sit and go find a public area or bar. Have a drink and in no time you'll be in the cabin.