The AVMA has an article on this topic at https://www.avma.org/public/PetCare/Pages/pets-in-vehicles.aspx. It includes a chart that shows "Estimated Vehicle Interior Air Temperature v. Elapsed Time." They also have some suggestions for cold weather safety at https://www.avma.org/public/PetCare/Pages/Cold-weather-pet-safety.aspx.
You might be interested in this article, as well: https://www.canidae.com/blog/2016/08/is-there-a-safe-temperature-to-leave-a-dog-in-a-car/