1) re: 2 versus 7 d/wk.
check out this thread, where robb notes some have found success on 2 d/wk fast.
"Kelly Starrett of CF San Francisco did IF on tues and thurs. He waited to eat his first meals those days till like 1-2pm. He noticed improvements in body comp and performance. It was not that hard to do. he is wrapping up grad school, runs a CF facility and is a dad and husband. Good enough IMO! So the take home message is do what works for you. Start with that base of good paleozone nutrition and tinker form there. Start conservatively, especially since you are in school."
2) also, i wrote in on robb's blog re: length of fast (as in a PM article, he suggested the 15 hr "cutoff").
"There is no magic with the 15-16 hr fast other than it seems doable and folks report positives such as improved leanness and recovery. I think ANY move in the direction of fasting or intermittent caloric restriction appears to offer benefit. How much benefit? No one knows yet but on a daily level it appears to simplify ones eating schedule. Everything else being equal it may be worthwhile for that point alone."
in short, 2 d/wk will likely be better than none. try and see, add more days and increase fast window as its doable for you!