Take if from a Texan.... 90 degrees isn't exactly extreme heat. This time of year, having a high under 100 means we've had a cold front. [8D] On a sunny, August day down here, you really can fry an egg on the hood of your truck. I've shot bows in temps up to 118 with no problems. As far as the bows were concerned, that is.
Your bow isn't really in trouble unless it gets too hot to touch, and they can easily get that hot when leaving them inside a car on a hot day, even in the trunk.