1. Turn the dial until the triangle (the one that points towards to the top right corner) is pointing at the current time. Make sure you turn in the direction indicated by the arrow, which is clockwise on the timer I have.
2. The dial that you just rotated is surrounded by gray plastic tabs at each 15-minute interval on the timer... for the period where you want the lights on, flip the tabs down.
3. Flip the switch on the top of the timer to timer mode, which I think is left, but I'm not using mine at the moment to verify.
There are 2 tabs on timer one will turn on and the other will turn off when lever on tab rotates around it catches on a trip dial so you will need to turn it in direction indicated to see which one is which pull tab out and set it in the time slot you want and same for turning off.