Day after, in the morning, before I passed any stones. I didn't make much mental note. It was no big deal. Definitely not in place of Epsom Salts . Huge flush that day, though I doubt the CS really had much effect (if any). I started passing stones long before it could do anything special. I don't think it's important. I take CS almost every day, and, IIRC, it was more reflex than any plan.