Also, with Hardy board, I would be overly concerned it it has dried. Theres really nothing to rot, and the moisture will find its way down eventually. I sure as hell wouldnt caulk wet wood, but back in Reno, we would sometimes start caulking the driest side the day we powerwash. Its a little different in the desert of course, but all in all, Im more concerned about the moisture content of the wood itself, than if a little bit gets behind the siding or trim. And its not like you're painting over wet surface, you're just caulking joints. If you cant visibly see water in the joint to be caulked, I'd caulk it. Obviously, its preferable to let it dry though, but sometimes that would be a waste of a half day.