Hi StevieT, Welcome to Cruise-Chat!
The latest I've stayed on the ship was a little after 10AM. You'll have plenty of time for breakfast, showers, etc. Just ask the steward if you can stay in, and if so how late before he/she needs to clean the cabin.
My best advice is to pack the night before and use Carnival's Luggage Express service. I believe it is $20 per person with a limit of 2 bags each. They will issue your boarding passes and take your luggage to the airport to be checked in.
and type in "luggage express". It should be the third item for the details.