We just took a tour organized by the Panmunjom Travel Center - specifically the tour with a North Korean defector - that I highly recommend.
http://www.koreadmztour.com/program/program_1.asp
It leaves at 9:30 (check in at 9) from the Koreana Hotel, visits the JSA after lunch and is back in Seoul at 5. While not a late morning departure like you were looking for, I felt there was little "fluff" during the tour and the opportunity to speak with someone who until recently lived in North Korea was quite insightful.