CYA won't really pre-dissolve very easily. It would take days before it did. At least any time I ever tried, it didn't. I would wait a week before retesting. No hurry. Better to go slow than retest too soon and add some only to find a few days later that you have overshot your target.

And, Carl is right. No easy way to lower cya without draining and refilling.

I, too, put some CYA in a container of water and left it out on the deck, shaking it every few days and mine didn't totally dissolve either.