The starting point is: on a one water valve system you should run it 4 hours a day. On a system with two or three water valves start at 5 ½ hours a day. New pools with little or no landscaping or extreme weather conditions may require more time. If the pool is cleaning properly then you can reduce the cleaning time by ½ hour amounts until it is not doing the proper job, then go back to the amount of time that worked.   Note: the answer above is based on the water valve having the proper pressure. The normal range is 17 to 25 psi. The pressure may vary than this range depending on what PSI it takes to properly clean the pool.