Why hotter than normal? Learning is all...
DE is like microscopic glass. It cuts insects up and bothers their breathing. When it is hotter outside, they dry up faster from the fluid loss. The DE cuts up their soft tissue as they try to eat or transverse foliage. Spreading it on the dirt keeps the crawlers out too. After a while the bugs generally avoid that area of the yard.
I can watch the bugs jump off on a hot day.
As far as i can tell DE doesn't burn and I can apply it in the morning in the sun when the bugs are most active. Every week or so, depending on if it was windy.
Neem is best sprayed at night and you can only spray so many times before it burns the plants, and stunts them, in my experience.