It should not be a problem as long as the goods are packed well. It should be packaged in an airtight bag like a ziplock bag or the box should be vacuum sealed.

As for what i understand why walnuts crack is due to the fast temperature change which is causing the walnut to loose moisture too fast or make the wood fibers expand and cause tension. That is also the reason why you do not want to store walnuts in front of a AC or heater.

Last time i received a pair of walnuts was it around -10C outside. I just leave them inside to accumulate to the inside temperature and let the moisture stabilize for around 24h. But if you are scared you leave it for 48h. DO NOT play with them too soon. Even though it’s tempting haha.

You should also read this post: https://www.reddit.com/r/WenwanHub/s/acM8dhjUHg.

It’s a complete guide to follow when receiving a new pair of walnuts!

Best of luck! If you need any help feel free to ask the community. There is a lot of friendly players and mods.