Things are very different when you are leaving MCO after landing, and when you are returning to MCO to go back home.
When you fly into MCO, you do not have an appointment for a specific DME bus. You need a reservation, but they do that just so they know about how many people are going to which resorts at about what time, so they can plan accordingly with staffing and buses and dispatching and routing. It's not like they are planning for you to be on bus #7 and you could miss "your" bus by arriving later than if you had gone there directly from your airplane.
In other words, you could land at MCO and shop for HOURS ... it's not like anyone is waiting for you, specifically you, to show up. As long as you have a reservation, you have a ride. The only exception would be if you are arriving very late at night ... you want to make sure that you make it to the DME Welcome Center before the person who has the latest reservation of the night. DME is a 24-hour operation, but only inasmuch as they are expecting people due to reservations; they also automatically track late flights. In other words, if there is NO ONE with DME reservations landing at MCO after, say 12:15 a.m., and everyone from flights all the way back to like an hour before that have already checked in and are on buses, the DME desk will shut down for the night. If your flight arrived on-time at 8:00 p.m., they won't be expecting you to check in at 12:30 a.m.
But except in that weird and totaly hypothetical circumstance, you can check in and then board a bus any time you feel like it. Just make sure you go to your bus right after checking in. Don't check in at the DME desk and then leave the area and come back.
Now, on the way back to the airport on your way home, it's a completely different story. For that bus ride, you ARE assigned a bus pick-up time, and if you are not ready for it you WILL miss your bus. More details on that if requested ....
