How long do you need to exercise per day to be healthy?

20+ minutes. 20 minutes or more, non-stop, every day. And remember 40 today does not equal 20 today and 20 tomorrow. If you do 40 min today, you still need 20+ tomorrow! Go for it.
30 minutes. The minimum recommended is 30 mg 3 times a week- graduakky working up to 1 hour 5 days a week.