Interesting. I just mix up a new batch right after a WC and let it sit for 2 weeks. It's always good to have some saltwater on hand, so if there is an emergency, I can add it.
Not sure about the caustic non-dissolved salt argument as I've never seen any convincing data on it. Maybe true, maybe not.
However, it's good to let it sit with a powerhead and heater, so things can stabilize to a steady state. Then you can add more salt or water as needed to hit your target.