How long should you exercise in a day?

Varied opinions: Depending on your overall health, medical condition and need for exercise, even as much as 10 minutes of any kind of exercise 3-7 times a week can make a difference in your health. Certainly the more fit one is, the more exercise can be done. I would recommend 30-45 minutes 3-4 times a week and more if can, to keep you at your best health. Speak with your pcp, personal trainer or qualified prof.

That depends: How long you should exercise depends on things like what is your level of health? Your level of conditioning? Which activities are you doing (vigorous, light exercise, lifting etc)? What is your goal? Someone who has a goal to run a marathon will likely require a different amount of exercise then someone who just wants to stay aerobically fit. There is no "one answer" to this question.