Customers refer to advice they’ve read online about the wisdom of painting in summertime, and so ask this question frequently.  A lot of “experts” online are not really experts, and more often have no practical experience in the craft.  The paint doesn’t know it is 95 degrees outside. We plan our day to work ahead of the sun. This means we start on the side that will be the hottest and try to stay ahead of the sun’s progression through the day. Or, we just work on the shady areas. Temperature is not the issue. Full sun is what needs to be avoided because it can dry the paint before it has a chance to level out or be back-rolled or back-brushed after spraying.