Will hot car ride kill a guinea pig?

I plan on adopting a guinea pig in the next two weeks, and I want to know if the guinea pig can get heat stroke from the car ride home. I live in TX where it has been in the high 90s, and I am not sure if an air conditioned car is enough to keep the guinea pig from getting sick. Should I pick him up at night or early morning, or will this stress him out? I've read several books and I haven't read about this. Anyone have any advice? Thanks. :)