I get my eggs from the same seller. Actually snow is an insulator so they may be fine They pack them really well, too, inside the egg carton. I've had UPS put mine in my cold barn right inside the doorway, no doors, and they were there overnight and I had a 100% hatchrate.
What I do with mine is set them on top of a warmed up incubator. I have 24 eggs, from them, in the incubator right now and 23 out of 24 are fertile and going strong. This is the 4th set of eggs I've gotten from them. One set I actually went to their place and got when I was in NY at Christmastime so I got to see their Call ducks, their ponds (they have 4 of them) and their whole set up. It was nice.
Laurie