Just started to get my diet back in check today...Have ran or done cardio within 6 months...Haven't lifted in 2 months...

Got about three weeks until the test and plan on learning on a threadmill...

How many times a week should I train? Should I ever do twice a day?
What exactly should I be doing to train?

I've heard a few suggestions of websites...
Run at "X"MPH on the treadmill until I can't anymore?
One minute walk at "X"MPH then three minute run at "X"MPH, cycle for 30mins...
Something else?