This webpage is based on Revision 30 (Oct 15, 2014) document Updated NSE PhD Requirements - OCT 2014.pdf
Typically http://web.mit.edu/nse/education/grad/phd.html is supposed to have reflects the Oct 2014 revision, which is the most up-to-date information, though currently (July 2015) the website reflects May 2013 version, so you should refer to the Oct 2014 document linked aboveversion as of summer 2016.
Typical Timeline For Taking courses
...