In an article on the WebMD website, they suggest that 30 minutes a day exercise may be the magic number for weight loss.
The study they mention is quite surprising.
Moderately overweight men who exercised for 30 minutes a day (enough to sweat) lost an average of 8 pounds over a 3 month period. Men who exercised for 60 minutes a day only lost 6 pounds.
One of the benefits of only having to do 30 minutes a day is that you will have more energy during the day than if you exhausted yourself with 60 minutes. So, there are fewer obstacles to keeping the weight off.
Read the report.