The issue I see, besides the dates being very close together, is - a month before graduation? Really?? Holy Distraction, Batman! I would not be happy, as a parent, with that date, either! I'd prefer that he is free to concentrate on his schoolwork, and not have to worry about the stress of dealing with a wedding in his final semester. When I was in college, my father died unexpectedly in April of my junior year. It was really tough finishing my work that year. I also remember that last semester being very tough, as well, with a huge senior project and exams, etc. I remember even being afraid to look at my last grade posted because I was afraid to think of what I'd do if I hadn't passed. Point being, there's already so much stress in college, why knowingly add to it when waiting a few months - or even a few weeks if she also wants to say she's a 2017 bride - would take a lot of the pressure off and wouldn't partiularly matter much in the long run?
To answer your question about interference from in laws, mine were always really great about not interfering - until we were planning our wedding. They had some ideas that were different than ours, made them known, we discussed them, then we moved forward. Glad to say that in 36 years, that's about the only time they ever did that, so just because future MIL has some concerns now, it doesn't means she's necessarily going to be a horrid MIL.