Welcome back, Jeff! The time to which you are referring is actually your
Port Arrival Time. Disney asks guests to select from available Port Arrival Times when they begin their online check-in, so that the ship has an idea of when to expect you at port.
That being said, since you have the latest port arrival time, I would highly recommend you plan to arrive earlier than that. You wouldn't want to plan on 3:30, only to run into a delay getting to the port and then miss the ship. If you arrive earlier, and other guests have already checked in and boarded, you'll certainly be able to board. You may have a short wait, since they weren't expecting you at the earlier time, but most likely you'll be able to head onboard shortly after arriving. However, I wouldn't go too much earlier, maybe 1:30 or so. By then, the crowds will have died down from when the boarding first began, and you shouldn't find much wait. Bring some snacks and activities to entertain your boys, as you may have to wait in the terminal for bit until your boarding number is called. Then, once onboard, you can head straight to Cabanas to get a bite to eat! If your boys want to go to the
pool right away, pack their swim suits in your carry-on bags, and change in the restrooms onboard near the pool deck. Then you can play and swim and grab a quick bit to eat from one of the quick service spots on the pool deck. It's a great way to settle in and begin your magical cruise with Captain Mickey and his crew, Jeff! My kids love to head straight to the pools before they get crowded, so we always toss our swimsuits in our day bags!
There's nothing better than walking onto the ship for the first time as the Cast Members announce your family name and applaud your arrival, Jeff. That embarkation day is going to be so magical!
Marcy