So I just started a new job at a college campus. My office is right across from the gym, and my hour lunch is way too much time to just eat. I am thinking about doing a quick 20 minute workout, with a 20 minute shower/dress, and a 20 minute lunch time. First, has anyone ever tried anything similar? Second, I am 5'10" and 170 pounds, I am looking to strengthen my core, and drop some of the excess pounds, what would be good routines for a 20 minute daily workout?