It is best to aerate at night and perhaps just a little after dawn during high summertime temps. This allows stratification during the day. If you schedule the start say around midnight ... a good portion of this heat will dissipate. If the night air is cooler than the pond, aeration under this condition will cool the pond.

OK, but aeration isn't the biggest problem you face. Sounds to me like you have a very large standing weight of fish in BOW. You are going to need to manage that aspect or the pond will manage it for you with fish kills like you observed. Going forward develop a plan that institutes a yearly minimum harvest and that will keep your standing weight below critical thresholds of carrying capacity.