I think if everything goes as scheduled, you might just make it. But if your flight is late getting in or there's a longer than usual wait for a DME bus, you'd be cutting it close. Now with the no-show penalties for dining, I'm hesitant to make first day dining ressies unless I'm giving myself a pretty wide berth of time.
Not sure if this is of interest, but I just went back and looked at our "stats" from our April 2013 trip.
Our flight was scheduled to land at 11:05 a.m.
At 11:25 a.m. I took a pic of the "New Fantasyland" sign just before you get on the airport Monorail - so it must've taken us about 20 minutes to get off the plane and make our way out of the terminal (and we probably made a quick bathroom stop for DD). From that point it was just over an hour to make our way downstairs, wait for a DME bus and ride to our resort. The timestamp on my pic of the entrance of POR says 12:27.
You'd also have to allow time to check in and go to your room to drop your things. Will you want to freshen up? If so that's a little more time. Then transportation to MK - not sure which hotel you're staying at but bus vs. monorail vs. walking (if you are at Contemporary) will make a time difference here.
Just my two cents! Good luck

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