Well it takes 3 months to build up enough in your system as it's a herbal extract not a drug, so think three months ahead.
I'm of the ilk, it's not going to damage you, so try and see. Stop if you don't like it. I've started taking it and noticed definite physical differences in my body, not so much with my cycle.
It may be coincidence, but my areola are bigger, my boobs fuller (I thought these were symptoms last month but got AF! And they never went away), so can only assume I have produced more progesterone, which is great. I have been moody though just seems to be settling down. Also had lots of cm this month, which again I feel is good as wasn't getting much (still only ever seen the elusive egg white cm once ever, but hey, you never know).
I also just started taking maca root, which you might want to read about. Boyfriend takes this too
they are meant to be ok to take with vitex, I've tried to read up!
Will just see what happens.....