It's one thing if you getting in at 6 am and have time but if you are getting in at 9 or 10 or later, then you really want to board as early as possible, if only to avoid the long lines, get yourself situated on the ship, have lunch, walk around and rest.
After the cruise, I'd find a dinner spot around your hotel because you will most likely be tired and just need some downtime from being stuck on a ship in a small cabin all that time.
Don't get me wrong, I love cruising but at the end I want to rest and have some personal space and plus at that point I don't' really care about food.