Long story short....12:00 is listed on the majority of DME vouchers, for arrival into MCO, simply because DME needs to know only that you are arriving that day...time doesn't really matter to them. Why? Because you aren't assigned a specific bus. Once you get to MCO, you may decide to shop a bit, or get something to eat. It could feasibly take you an hour or so to get to DME...depending on what you do along the way between the gate and the DME checkin area. So....DME needs to know only that you arrive that day.
Now...for your departure, ride back to MCO??? Yep, they need to know the exact time of your flight. This is what your DME pickup time from the resort is based on. You are assigned a specific bus this time. So, if you weren't able to give DME your exact flight info when you booked DME, call them and give them flight numbers as soon as you know them.
If you haven't done that, you can give it to DME when you arrive at DME and checkin for your resort bus....a lot of times they have questioned me about my return flight when I first arrived at the bus podium. Or, you can give the info to the front desk when you check in. Just don't leave it until too late. DME has to know your return flight info no less than 36 hrs prior to your departure...more than that is really better.