Closing time of Cable Car & Gate at Jinshanling Great Wall

Hello: I want to take sunset photos of the wall on my visit in December. Sunset time is about 5PM in December. However, I am not sure how late they will let me stay up on the wall. My questions are:

a) How late in the evening can people stay up in the General's Tower Area of the wall?
b) How late does the cable car operate to come back down? So, can I catch it after my sunset photos or is it too late and I have to walk down
c) How long does it take to walk down if necessary?

Thanks so much !

SR