Yup, most definitely overnight. I've received quite a few reptiles, and heavily researched things, so I know how the whole process works, this will just be my first time packing them up... actually scratch that, it will be my Mom packing them up, since I'm the one out in Georgia, so I'll have to coach her through it (egh, I'm soooooo nervous).
I think I'm just terrified of accidentally cooking my reptiles because of over-compensating for temperatures that will only be at the point of origin. I'm not sure where the hubs are exactly (guessing Denver, and then another midway in the country), but I know for sure that every other point along the route is guaranteed to be warmer then where they're coming from, which is right in the middle of the freezing cold mountains.