Confused about when the UN General Assembly takes place, look no further than to this ammendment of paragraph 1 of resolution 57/301 of 13 March 2003 - clear as crystal:

“The General Assembly shall meet every year in regular session commencing on the Tuesday of the third week in September, counting from the first week that contains at least one working day.” In paragraph 2 of the resolution, the Assembly also decided that “the general debate in the General Assembly shall open on the Tuesday following the opening of the regular session of the General Assembly and shall be held without interruption over a period of nine working days”