We like getting to the terminal early, usually around 11am. We get checked in, look around, get in line, take pictures, watch mickey mouse cartoons, go outside and look at the ship. Before you know it you are boarding that magnificent ship, your family is annouced on board, wave to Captian Mickey. We then do the ressie rush (for us it's just palo brunch and signing the kids into the clubs before the line gets long). Then we drop our carryon bags in the room and up we go to lunch. After lunch we walk around and explore "our ship" or go swimming. We start unpacking a little before 4 (manditory life boat drill) and finish unpacking after that.
There are many things to do - especially if its your first cruise on this ship. Getting oriented - that's a big job - it's easy to get lost. Eating - might as well get started early on that

There is a guided tour of the ship. There are excursion and shopping talks. There's the swimmimg pools and the sports deck (shoot baskets). Theres the spa tour.
I believe that "all aboard" is at 3:30. I know that people do arrive up to the time the ship pushes off of the dock (late flights or other delays and just some clueless people out there). All services including the pools shut down from 3:30 to 4:30 because of the manditory safety drill.
So yes, there's things to do onboard before the ship sets sail at 5 or 5:30.
is there a parking place to leave the vehicle close by and how much is the fee for that??
When you arrive at the port they will tell you where to park and I believe it's $10 per day.