I had an AP before and got it validated at DTD. This time we want to go straight from checking in to MK. Can you get AP's validated there? If so, is it at the regular ticket counter?
You can go to MK and get it validated at the guest relations window to the right of the park entrance. We got ours done there when we arrived last Oct. Didn't take that long. Although, there were no lines at the time. Maybe 10 or 15 minutes. Not bad.