How long is the walk from Jinshanling EAST gate to the Jinshanling rest area ??

If I take the Beijing - Luanping public bus at 7am to Jinshanling rest area,how long is the walk to the WEST gate?
I don't have a proper map. I want to walk from WEST gate to EAST gate on the wall to exit.
So I need to know how long is the walk from the EAST gate to the rest area at catch the last bus back to BJ??
The last bus back is at 5PM (17:00),right?
If I miss the last bus back,can I just flag down any bus going to BJ?
Is the hard to do? are they many or few buses passing back to BJ?