Hi Lilylou,
The reason you take vitex in the morning is because of its effect on the pituitary gland.
I have studied herbalism, but I am not an accredited herbalist so I am not giving any sort of professional opinion. Vitex is, as I said often given to women who are threatening to miscarry. Once you have ovulated you are already in the luteal phase. If your progesterone isn't high enough then a pregnancy cannot be sustained. So it makes much more sense to be taking the vitex all through your cycle.

I consult a naturopath/herbalist regularly and I have a tincture that includes the vitex. She recommends that it is taken for the whole cycle. So, I feel sure that you would be very safe in taking vitex throughout your cycle. If you start it after ovulation it wouldn't be enough time for the progesterone to build. Do a google on progesterone levels in a menstrual cycle and you will see how the ebb and flow of the hormones goes. Just before ovulation the progesterone rises. The value of the vitex is to ensure this rise and that the rise is sustained. Could you consult with a herbalist/naturopath? It would be worth a visit and then you will feel comfy with what you learn. I understand that often we have our own ideas and they can differ a bit. I am just sharing what I have learnt to be so!

Try and take that b6 it is really helpful in conjunction with the vitex.

Good luck, keep in touch!