I run mine based on the cost of the electricity ... In my area rates go way down between 9pm and 9am so I run mine on 2 cycles 9-12 in the evening and again 6-9 in the morning. If I did not need to run the pump to generate chlorine I could probably get away with one 4 hour cycle to keep the pool clean and I'd do that in the middle of the night.

In Vegas it probably helps to keep the water temp down if you run it at night too..