NSE's official site http://web.mit.edu.ezproxyberklee.flo.org/nse/education/grad/phd.html contains the most up-to-date information concerning curriculum and exams.
Core requirement ("the modules"):
Pass the modules with satisfactory grades. Refer to the "Threshold Requirements for Undertaking Doctoral Research" session of the above link for details about the GPA requirement.
Oral exam:
Reference: http://web.mit.edu.ezproxyberklee.flo.org/nse/pdf/education/Procedures_for_the_Oral_Exam.pdf
- Starting 2015 offered twice a year (beginning of Feb, end of May). In 2014 oral exams were scheduled Feb 3-12, 2014.
- Roughly one hour for answering the 1st question (prepared question), another hour for the 2nd (mandatory question).