enlisting in the army need workouts

[assault44]

I am enlisting in the army in 2 years and am incredibly out of shape{can barely run quarter mile} but i would like to be able to lose 90 lbs and run 3 miles in 12 minutes. For the life of me i cannot think of workouts that i can fit in my schedule which consists of going to school at 0645 or 645am and coming home around 1600 or 4 pm