Yes you can - and even earlier than that!! Generally after 10.00/10/30am you can board - and it is an excellent way of touring the ship whilst it's quiet. Lunch is provided in the Windjammer. Be aware, though, that you cannot access your cabin until well after 1.00pm, so if you have a lot of hand luggage, coats etc, be prepared to lug it around with you (we learnt the hard way!!).
Staff are also usually available for bookings for the spa treatments etc etc. Go and look at your table in the restaurant because there'll be an opportunity to change it if you wish.
Have fun! - Alison.
We arrived at the terminal at 11am and were on board by 11 30am, well worth getting there early. enjoy it.