Getting started, 30-45 minutes a day, 2-3 days a week is plenty. Put 1 day during the weekend, and you've got 30 minutes during the work week to find. I know its not always that simple, but being healthy is important. With all the hours we give to our employers, out friends, our families, take a few each week to give to yourself. It will improve your time with the others.
Anastas Dimitar Martin