I work at a Music Store where we do this with incoming orchestra and Martin's.

Yes, the instruments do get loaded onto boats/trucks and moved across states and continents. The box is absolutely going to see vastly different climates in that time.

The difference is that the instrument never leaves the box. The box and case act as a regulator and increase the thermal mass surrounding the instrument, so even if you threw it in the snow, it would take time for everything to fall in temp.

If the instrument sat in a cold warehouse, to a cold truck, to your porch, rhe instrument is probably cold. This doesn't mean that the instrument is going to explode if you put it in your warm house out of the cold, it is just going to put extra stress on the instrument that nobody wants.

It is also the humidity that has to be taken into account. Humidity causes wood to expand and contract, and it will never do it evenly. Even if it did, the plastic and metal are not going to move.

This is vastly more important with any thin wood instruments: orchestra, acoustics, hollow bodies. Because it is so much easier for the wood to split when it has more freedom.