1,279. When the Molad for Tishrei Falls After Noon

Hilchos Kiddush HaChodesh 7:3

Let’s say that the molad for Tishrei falls at noon or after noon so that Rosh Chodesh should be the following day but the following day is a Sunday, Wednesday or Friday (days on which we do not allow Rosh Chodesh Tishrei to fall). In such a case, Rosh Chodesh is postponed another day, to the third day after the molad. Therefore, if the molad occurs on Shabbos after noon, Rosh Chodesh is set for Monday. Similarly, if the molad occurs on Tuesday at or after noon, Rosh Chodesh is set for Thursday.

Hilchos Kiddush HaChodesh 7:4

In a regular year, when the molad for Tishrei falls on the eve of Tuesday (i.e., Monday night) at nine hours and 204 chalakim (3, 9, 204) or more after nightfall, Rosh Chodesh is postponed. Rather than being set for Tuesday, it is set for Thursday.