Reply To: Putting on Tefilin on Chal Hamoed

I just remembered that they are certain rules for postponement of Rosh Hashanah see Rambam Kidush Hachodesh 7. This is made up by the designation of Cheshvan and Kislev whether they choser, molei or kesidron. See the calendar in the Tur in Hilchas Rosh Chodesh just before Hilchas Pesach.