Hi there, I had to take two cycles of Seraphene (same as Clomid) to conceive DS1. From memory, I had to start taking the meds on Day 1.
Anyhoo, I had to have constant blood tests to monitor and pinpoint when O was going to happen. Then again, my cycles were up the putt and I could never predict when O day was. The blood tests were also to done to get a better picture of how many eggs were likely to "pop". Too many, and you're told to avoid sex in order to avoid multiple pregnancy.

I assumed anyone who took Clomid/Serephane had to have blood tests done also.

Guess the point I'm making is rather than try and predict when O will happen, couldn't/shouldn't you also get bloods done to be accurate? Just throwing this out there - sorry I can't help ease your confusion any further.

Good luck.