Kind of adding to what JoshSloane said, I like to keep my hotspots so they don't exceed 90. Many reptiles will actively seek shade and hide or even burrow when temps start exceeding 85 degrees. Remember in the wild these snakes are rarely out when the sun is up as they are nocturnal. They would not be exposed to the heat of the day or even increased surface temps since the sun would be down. And once out of their daytime hiding places, the surface temps would be in a constant state of decrease until they returned to their hides to avoid the next day cycle. So even if the ground surface was 90 degress when they crawled out, it could be as low as in the 70's toward morning.