Yes, you can go and back in one day. The lodge near the wall is not very convenient, and it is not safe to camp on the wall. There are many passing buses taking you back to Beijing. You can take it near the gate of Jinshanling Great Wall. The bus is available till six or seven in the afternoon.

It takes four to five hours from Jinshanling to Simatai. But it depends. You can slow down your steps to make it six or seven hours. Good trip!