When you book DME you give them your flight details. They will then base your pickup time on that flight departure time.
MCO recommends that you arrive at the airport no less than 2 hrs before flight departure. If you book a private car service, they will pick you up between 2.5 and 2 hrs before flight departure time. I usually have to ask to be picked up 2.5 hrs before...most want to do it at 2 hrs. And this gets you to the airport 90 mins prior toi flight departure time.
Some worst case scenarios...
traffic on the highway. an accident which ties up traffic. longer than usual security lines. slow trams to the gate area.
Will all those things happen to you? Probably not. But, only one time have i arrived at the gate with more than an hour to spare. And considering that most airlines start boarding about 35 mins before official departure time, that isn't a long time to be sitting around...barely half an hour.
If your flight time is 8:25, you will barely be able to use RAC that morning. Not sure if that matters to you. You do have to have your bags checked, boarding passes in hand, and walking away from the counter no less than 3 hrs before flight time. So you would have to be at the RAC counter when they open at 5am to be sure you are done by 5:25.
Then, lets say they give you a pickup time of about 5:30...give or take....yes, you may very well stop at other resorts, or you could be the last resort on the route. No way of knowing beforehand..hence the 3 hr window. Then, the drive to MCO takes about 30 mins...so let's say you got picked up at 5:30, the bus stopped at one other resort, then started the drive to MCO at 5:50. You will arrive at Side A of MCO by about 6:20ish....depending on which airline you are flying this could be where you get off. Then, the drive over to Side B...now it's 6:30. There's your 2 hrs before flight departure.
Now...up you go to check your bags (if you haven't been able to do that at RAC)...now it's 6:45-6:50. Off to security you go. The line is moderate so it only takes you 20 mins to get through...now it's 7:15 or so. Wait for the tram to the gate, then walk to your gate..now it's 7-7:10. You get to the gate with about an hour before boarding starts.
And this is 'best case' scenario. Many things can happen to add more time.
If you give DME incorrect info regarding your flight departure, and then you miss your flight, DME is not responsible. Just something to keep in mind.
This is the big reason I won't book a flight home before 10am..no way am I getting up at 4am to leave WDW. I much prefer to sleep a bit, not have to worry. With a 10am flight, I am picked up around 7ish...time for me to get something to eat and get down to the bus stop after checking my bags with RAC.