I highly recommend cardio, and if your knees and feet can handle it, running, especially if you did run in college everyday. Start with baby steps with a high walk to log ratio. By 6 months in, you should be able to be at all run. Its great because 1) its getting warmer out, and for 6-8 months you'll have optimal conditions and 2) with your long hours, its something you can do at 3AM or 3PM.
You'll need to eat foods high in protein after your runs, and moderate carbs before (at least an hour or two). If you can manage, cut out wasteful calories (milk in your coffee, any added sugars, and dare I say...alcohol). When I want to cut up, I just stop drinking for a month and it helps incredibly.
To help aid definition you can do simple body weight exercises like push ups, pull ups, crunches and squats (no need for any weight while you start). I add these into my workouts at my stretch breaks during my runs.
Anyway, good luck man, and once you get this, not only will you look better, but you'll feel better too.