The night before is not an option because you have to check your luggage within 12 hours of flight time, but no later than 3 hours before your flight time. You will have to check your luggage in the morning, but RAC opens at 5:00 AM. You must be completely finished with the check in process no later than 3 hours before your flight departure time.
Give yourself some extra time. Usually we've gotten our luggage checked in quickly, but there were times when the line was fairly long and it took longer than expected. Definitely plan to be at the DME bus stop 15 minutes before the time listed on the paperwork you receive just in case the bus arrives early. If you are still waiting in the RAC line, take your luggage with you and check them in at MCO.