I discussed this idea of turning the aeration off during the day with a few aeration people when I was in the market for purchasing my diffused aeration. I was told by more than one that running it 24/7 will not overheat the water and that the difference in pond water temps running 24/7 v only running at night is negligible and not worth the effort and wear on the pump to turn it on and off. Thought it might save a little on the electric bill.

I'm no expert, but my understanding is that the point of running aeration is to homogenize the entire pond and so therefore turning it off if you pond isn't being completely mixed is somewhat defeating the purpose of aeration.