I'm not sure with a vinyl liner, but I wouldn't let it go too long. That's why I always start to bring it up the next day - if all the stains are gone. It will take a while for it to stabalize, so you have to test it a lot. Check your Alk too, you have to get them both in balance so they become stable. Use baking soda if the alkalilnity is low, and use borax if just the ph is low.