Arrive the day before. For our last cruise, we were delayed in ATL and just made it to the ship DURING the safety drill. We were checked in at MCO at the ME desk, boarded the bus, got there as fast as possible and almost ran through the terminal to board the ship. No "Welcome so and so family" just "get to you safety drill check in spot". Never again will I arrive the day of. Ever.
It is quite remarkable though that our luggage made it onto the ship. I was convinced I'd be shopping on board for clothing for that cruise!