It's going to be like any other mechanical timer. It has 96 tabs on 15 minute increments. They need to be set in the proper position for on and off times. Right now they're all in the down position on the dial. Half need to be moved to the other position but I don't know which is on or off with that particular timer. You'll need to figure that out. Set the timer to the time. 6 would be 6:00 am and 24 would be midnight. Once you identify which position is on or off move half to the off position based on when you want the light to be off.