Don’t confuse dehusking with shelling. The former can be done right away, but then, yes, the nuts ought to be stored for a while (in a squirrel-proof location) before shelling. Hadn’t heard of the nail trick. There are actually commercially available black walnut crackers — I always wished we had one. But I don’t imagine they’re any quicker than using a sledge, which can constitute a fun challenge: hitting it so it splits just right.