I was advised to start taking 600mg 2x a day starting on CD 6-12. I've been known to O on CD 10, so I think that's why they have me start so soon. I think 4 days before you normally ovulate would be enough. An actually since I've been ovulating later thanks to Letrozole, I decided to start taking it later. Otherwise CD 12 would come and go and still wouldn't have O'd yet. To sum it up, 4 days before surge and 2 days after.