97:10 One does not sanctify the moon until at least three days have passed from the molad – i.e., the moon’s first appearance in Jerusalem; some people wait seven days. If Saturday night falls before the seven days are up, we don’t wait. Rather, we sanctify the moon after Shabbos. We only sanctify it up to half of 29 days, 12 hours, and 793 parts (chalakim – 3 1/3 seconds), which is 14 days,* 18 hours and 22 minutes from the molad.
97:11 One does not sanctify the moon before the ninth of Av. Similarly, one does not do so while he is a mourner unless he won’t finish his mourning until after ten days* have passed from the molad. If such is the case, then he does sanctify it during his mourning period. One does not sanctify the moon after fasting until he has eaten something. However, following Yom Kippur we sanctify it immediately because we go out from shul full of joy from having our sins forgiven.
*”Days” in these cases means 24-hour periods from the first appearance of the moon rather than calendar dates.