Yes, you can board prior to the time listed on your SetSail pass. However, keep in mind that your stateroom won't be ready until at least 1:30 or so. With that in mind, your carry on bags will have to remain with you until you can get into your room.
I wasn't sure if you were planning on bringing a bag to carry onboard the ship, but I would definitely recommend it. In that, I would put at the very least a swimsuit, your evening attire for dinner that first night, and any medication you need throughout the cruise, on the off chance your checked luggage gets lost. The reason I mention putting your evening wear for that first night in your carry on is that there's a chance your luggage might not get delivered in time before you have to change to go to dinner in the dining room.
2007 - Majesty of the Seas
2009 - Enchantment of the Seas
2010 - Freedom of the Seas