Hiking the middle section of Jiankou Great Wall

Hi!
I would really like to hike the middle part of the wall, how long will it take to hike the middle part of the wall? I'm just worried about hiking the middle part and not having enough time to make it back to the bus station before the last bus leaves to Beijing. We're only planning on spending one day to hike the middle part of the wall, and we are planning on taking the first bus out of Beijing.