CHECK IN TIMES

We arrive Rio de Janeiro from Miami at 8am, but our check in time on the Marco Polo is 3pm the same day. Other than using an airport locker or renting a hotel room for 2 days (including 1 day before arrival because of the hotel check in /out times), can anyone suggest what I can do with the luggage while looking around Rio a bit? I noticed others saying you can check in your luggage early on some lines. Could we actually do this, say as early as 10am? Or since the ship does not depart port until 5pm the next day can we check in on the second day and just stay in a hotel the first night without even going to the ship terminal? Thanks for any help. [/b]