applying the second coat of flat exterior paint

Dry to tge touch.

I second that Dry to touch.never had a problem yet

In that kind of heat and hour or two should suffice. However, darker colors are different, especially low coverage colors like red or yellow. The longer you let them cure between coats the better. Applying a second coat before the first has cured sufficiently can cause rewetting of the pigments and ruin the hide of the paint. That results in more coats of paint to get it covered. This isn't usually a big issue in light colors, but the more pigment that is in a color the longer it takes to lock those pigments in.

I try my best to plan my days so that I am not recoating within a couple of hours, even though it is dry to the touch. Of course some days this can't be avoided. I am sure in the temps you mention you will be fine.
However some paints can not be recoated for a certain period of time.

I just recently used industrial urethane alkyd enamel, this can not be recoated for 18 hours even though dry to the touch in 3 or 4 hours.

Recoating too fast can also cause sagging, as it rewets the first coat. Dry to touch does not mean that the paint has properly cured. As mentioned, dark (heavily tinted colors) will cure slowly.