Is it in transit or sitting in a parked truck? Cold is not good for the bass. The neck could warp.
I said "could". I used to travel with my basses in the back of a truck with no adverse effects (before I wised up and decided to take better care of my gear).
What is too cold or too long will vary, depending on the specific instrument and other factors. BUT ... what can you do anyway? If the bass is damaged when you receive it, file a claim against UPS.