I think cd 12/13 is probably fine. My Napro Dr. did bloodwork every other day for an entire natural cycle to see how my E2 levels rose. Then closer to O she started watching my LH and then continued to check Estrogen and Progesterone until I started a new cycle. I did an ultrasound on Cd3 and then again on DPO+7. She also checked my FSH on cd 3 and DPO+7. Even though my estrogen rose to 370 or so by O (which is fine for one mature follicle), she could somehow tell that my ovulation was not optimal by the way the E2 levels rose over a series of days and where my fsh level was on DPO+7.
My Dr's goal is to get one mature egg at O, I think that with the way your meds are being prescibed, they are looking at getting a few eggs. Which probably isn't a bad idea since so many of our eggs over 40 are abnormal.
I've taken it both morning and evening. I've also divided my pills up to 4 on Cd2 and the other 4 the next day. I was told I could mine or either cd2 or 3.
Your numbers are so much better mine. when I did the monitoring cycle above my fsh was 7, my AMH was .16
Good luck in whatever you decide to do. I know it's scary when your not sure if you will be doing more harm then good. I'm kind of in the same boat this cycle. I just had my third lap on Mar 6 and I had a picture perfect cycle this month unmedicated. Even though I have the go ahead to go back on Letrozole tomorrow, I'm wondering if it would be better to try al-naturale one month.