Both opinions are correct!
I know that sounds like a stupid answer, but there are a lot of trade-offs that are difficult to evaluate.
Cooler water is always capable of holding more dissolved oxygen than warmer water, so that is the first trade off. However, you have to circulate the water to keep it well oxygenated - and "de-stratifying" your pond increases the average temperature during the summer.
Dawn is usually the low oxygen point for a pond and also usually the coolest time of day. You better have good oxygenation beginning at some point prior to that time! That is either run 24/7 in the summer, or let the hot surface water radiate and have evaporative cooling for some period of time after sun down, and then have your aeration system kick on after x hours.
Every pond has a different configuration, different plant community, and different oxygen consumers in the pond. I would say the best way to determine the optimum for your pond is to buy a very expensive dissolved oxygen meter, and takes lots of DO and temperature measurements throughout the year. However, that is a ton of money and work.
The next best way would probably be to take the advice of a local expert. If you have a smart pond maintenance guy that also does a lot of other ponds in the area, he should have a good idea what will work for your area.
I like asking tons of questions (on any pond topic) on this forum. If you learn the
reasons for the trade offs, that will help you make a good decision on the few times where something about your pond will make it the exception to the local prevailing wisdom. There are definitely some aeration experts here that can give you excellent general and regional advice.
Good luck taking great care of your fishes!
P.S. Where can I get a GSP that points walleye? I can think of many times that would be very helpful!
