My opinion only, but I think it means that once the bean hull dries out, it would soak up the Sevin and make it harder to break down. It could also soak up in the dried bean itself. As long as the bean hull is green and not dry, it would only need the one day. Apparently sunlight is one of the things that helps break down the Sevin. But I admit, I have scratched my head on that one as well.

This must pertain to beans that are dried on the vine, But PHI is about harvest and, many times, for dried beans, you harvest long before any of the beans have dried. But then again, maybe seeds in general absorb Sevin more effectively than hulls or leaves? Fresh green beans don't have any significant seeds in them. I notice that corn and peanuts, which are seeds, as well as all legume seeds (e.g. peas and lentils) have longer PHI than anything else. That would be consistent.

That was also my guess! Thanks!

FWIW, I believe it is established that Carbaryl (Sevin) is not efficiently absorbed by leaves, but is very efficiently absorbed by roots, wherin it passes up into the plant. So it does appear to depend on the kind of tissue. It is true that leaves are covered with a hydrophobic cuticle, that prevents water loss. I have to assume that seeds, like roots, have a more permeable cuticle, because you want them to absorb water. That may determine the absorptivity of Sevin.