Question Is 11 Hours Enough for TourIstanbul and Customs?

I'm considering a flight that lands at Istanbul Airport (IST) at 2:10 PM and I have an 11-hour layover. I'm really interested in doing the TourIstanbul program, but I'm worried about whether this is enough time to clear customs, participate in the tour, and make it back in time for my connecting flight. Has anyone done TourIstanbul with a similar layover? How was your experience with the timing, especially with customs at IST?