One Extra Semester - Benefits? Trouble Planning
I would recommend eliminating the philosophy major in order to start your graduate degree in mathematics sooner.  It seems to me the philosophy major does little to advance your career goals; you described it as a hobby.  Taking an extra (presumably fall) semester to graduate will delay your career by a whole year because graduate admissions typically only occur in the fall.  The year you lose comes at the end of your career, when you will presumably have the best and highest paying job of your life, or can retire a year earlier.  On the whole, the costs of an extra semester seems very high compared to the benefits.