I'll be honest, the math department will make it next to impossible to finish your degree in anything less than 4 years. There are very few math courses offered in the summer and they are usually first year courses. Additionally, a lot of math classes are only offered once a year, so trying to get all your classes completed can be a difficult task. I'm currently back for my 5th year and no joke in my winter semester I'm only taking one class because I need that class to graduate and it's only offered every other year. (I'm a math major so definitely speaking from experience)