The pool heater can only run when the pump is circulating water through the filter. It should run for no more than 12 hours and it shouldn't run when the outside temperature is below 50 degrees.
To turn the heater on press the menu select button under the display (Photo 1) two times until you see the screen that says "HEATPUMP TIMER" (Photo 2). Then, using the up arrow button on the right of the display, advance the timer in 10 minute increments until it is set for the amount of time you want the heater to run. It should be set so that the heatpump turns off prior to 6 A.M.
Once you complete setting the timer, the menu will return to the first screen in a few moments, no other action is required.
You can advance through the menu display by pressing the menu select button one time for each screen if you go past the HEATPUMP TIMER screen while preparing to set the timer.