You get the most benefit from exercise if you do it for at least 30 minutes a day for 5 - 6 days a week. But you do not have to do 30 minutes in a row. Studies suggest that you get the same benefits if you work out for 10 minutes 3 times a day as you do during a longer session.
Update Date 5/11/2014
Updated by: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.