I've gotten Nep seeds in cold weather with good results. I think storing Nep seeds for any time is bad as they lose viability quickly. However a reasonably quick postal journey is probably ok. I always thought that they wouldn't freeze because there was so little water in them. You may lose viability but that usually manifests as a lower germination percentage. Since you usually get lots of Nep seeds, you should be ok. This only would be true if the seeds were fresh.
Of course, I would probably not buy very expensive seeds in February.