When it's excessively hot, temps like we're experiencing in Texas (it was 89 at 6 a.m. in Dallas this morning, on its way to 110), and you've run your aeration system continually, your water is as clean and healthy as it can be, based on the system. With extremely high temperatures, running the system at night helps take advantage of a lower mean temperature.
In other words, if you were to check the temperature every minute, write it down and then average it over 24 hours, that's close to the temperature your aerated pond will be. But, running it at night, that ambient temperature will be cooler, thus your entire water column will be cooler than if the system ran 24/7. For extreme heat as this, it can make sense to run it at night. Temperature becomes the issue rather than totally thinking about oxygen and water contacting the atmosphere.
