I completed my MPH in one year at BU. Its entirely doable. Most of the classes are offered in evenings or afternoons, as the school gears toward non-traditional students who are already working. During the summer, you can take some of the basic requirements like Intro to Epi, Intro to Biostats during the day. These classes are full of med students. FYI, at the time I did this, I worked full-time and I am a single mom.
Don't let the school try to dissuade you from pushing through in a year. Its not a big deal at all. BU is a GREAT place to network, you meet influential people from everywhere.
Good luck, either way.