By testing on days 12 and 21 we can assure ourselves that we are reproducing a normal cycle of a younger woman. Since the Basic Wiley Protocol rarely gets blood levels of more than 300 on Day 12, the blood work is a way of justifying to your doctor that you might need more to meet the upper levels to normal.  Day 11 or 12. Day 12 is better to see the estrogen peak. Check both estradiol and progesterone on both days. Day 21 is the progesterone peak but check both progesterone and estradiol. Try to do this about three or four hours after applying your cream. Don't put cream on the area where the needle will enter. Checking on both days 12 and 21 will show an inverse relationship between the hormones.