PhD in American universities has 2018 fall start and spring/summer start. Fall is the standard start date (starting from late-August to early September)，spring starts are on March 1st or May 1st of new year (if you don't need visa for that semester and can do a J1)，or January 15th if your master degree was completed there(which gives one extra week into Jan). Summer classes were optional until I started my Phd，but now they are mandatory with an average length of three weeks. You will have two courses every term as well as research. The regular duration time frame lasts about ten years total. There are also accelerated programs like MIT’s Master Program which takes just five semesters but still requires full immersion， it goes by "M".
You could be interested in this short video clip of our school where students are talking https：//www.youtube.com/watch？v=4JrqKcHkzRQ&feature=youtu.be
