I don't see why you can't start adding it now. It takes a long time to dissolve so you don't want to put it directly in the pool. I put mine in the skimmer (with a cartridge filter) and others use the sock method. As long as you don't take the cartridge out and clean it, the CYA won't get lost when you vacuum. Wait at least 5 days to retest for it. Congrats on getting your pool squared away.

Peter