With any stone it's a matter of how porous it is and some are more than others. The denser Norton 8K doesn't need soaking while the Norton 4K and 1K need soaking. Even after a 30 minute soak both of those absorb water. Similarly if you store them dry which I do, after use you have to keep them out to dry for days before all the water evaporates from them.

Many years ago I put the Norton 4K away a few hours after use thinking it was dry and when I took it out again weeks later it wasn't a pretty sight.