I'm not familiar with your aeratrion system so you need to make sure that it is large enough to give you one complete turnover during your scheduled nighttime run. The easiest way to figure that is to moitor the water temps. When you start the system up from scratch you will see that the lowest water temps will be cooler than the water temps at 18" deep. Once the water temps from 18" deep to the very bottom are within a couple degrees of each other...you pond has been turned over. That legth of runtime is the minimun that I would run. This way you are not just bringing up dead water and mixing it with the upper good water daily (or nightly). I also try to set my nightly start time to coincide with the time at which the outside abmient air temp drops below the water temp at 18" down. This helps guarantee that you are cooling the water not heating it. Likewise with the stop time...once air temps get above the 18" water temp, it;s time to stop the air. This maximizes the aeration runtime and minimizes the heating of the pond. We all know that the weather changes day to day, so I just set mine up to be close to the weeks weather and adjust as the weeks go by.

JP makes a good point about the pond's bio load or standing weight.