Is it possible to visit the Great Wall in the afternoon?

Well, according to your arrival time, you are not suggested to visit the Great Wall because of the limited time. Badaling Section opens from 06:30-19:00 and Mutianyu Section closes at 17:00. Although you hire a taxi, and go to the scenic area from the airport directly, the duration is 1.5 to 2 hours. So I'm afraid that you won't have enough sightseeing time.

If you still don't wanna stay at the airport, you can go to downtown area. There are also many popular attractions, such as Tiananmen Square, Forbidden City, Silk Street, Wangfujing and Qianmen Street. Meanwhile, you can easily find nice local snacks in these area.

Finally, remember to go back to the airport 2 hours in advance. :)