Just to add - we did this a couple of weeks ago, although out flight was 4.30pm and without any extra security.

We left the hotel (Grand Hyatt) at 8am. From there it took just under 4hrs to drive to the wall, take the shuttle up to the cable car, take the cable car, walk along the wall and get the toboggan down.

The walk took us 50 mins - the guide suggested most people took 60-70 mins. We had no meaningful queues.

Bear in mind you also need to buy lots of different tickets at different booths, which may add to the time it takes you.