The defense needs to be held before the GSAS dissertation submission deadline, and final dissertations must be submitted to the members of the Dissertation Defense Committee at least one month in advance to give them time to prepare their reports. This suggests the following timelines:
For a May Degree:
Dissertation due at GSAS by mid-May. Therefore, the defense must occur no later than early May (again, with final draft submitted at least a month prior).
For a November degree:
Dissertation due at GSAS by mid-September. Therefore, the defense must occur no later than early September (with final draft submitted at least a month prior).
Students can also apply for a March degree. The GSAS dissertation submission deadline for March degrees is in mid-January, which means that students aiming for the March degree will need to defend by mid-December, before the winter break.