I would not think breakfast because we don't know yet when the character breakfast will be. I am assuming there will be one and they are usually on sea days.
On previous cruises the time was usually around 2:30, since most people from the dis usually try to board as early as possible to get to enjoy the first day. there will never be a perfect time, so just post here when it's decided. Hopefully it will be a time most people can make it. We can wait and see the navigators to see if anything is scheduled the first afternoon or not and when the breakfast is. I know the sea day afternoons tend to have more activities.