Arachin 9 - No More, No Less
They never made less than four thirty-day months in a year, and never more more than eight twenty-nine-day months. The lunar month is about 29 ½ days, so some months have to be short, and some long. In the time of this ruling, beginning of a new month was declared based on the testimony of witnesses who saw the new moon. The Sages would also move the first day of the month slightly, for calendar purposes, but kept it within the above guidelines, so that Rosh Hashanah would never be too far off from New Moon.
The two loaves of Shavuot are not baked on the holiday itself, so they were eaten at least two days after they were baked, but no more than three days - when Shabbat intervened.
The bread of vision was baked before Shabbat, stayed on the Table in the Temple for the week, and was then eaten the following Shabbat - while still fresh and warm. Thus, they were eaten no less than nine days after baking, but no more than eleven - when two days of Rosh HaShana intervened.
A healthy child is circumcised not fewer than eight days after birth, but no later then eleven - when Shabbat and Rosh HaShana intervened.
Art: Rembrandt Van Rijn - Circumcision