It's impossible to say how long you should punch a bag. For instance, you can combine bag strikes with push-ups or sit-ups as part of an effective beginner's punching bag workout. From 20-30 minutes of punching a bag each day can provide many of the benefits. The average bag session lasts two minutes at the most. A professional usually punches and moves at high intensity for three minutes. I occasionally box for 4-5 minutes with the heavy bag. As a result, there are fewer rest periods needed, and you are given a greater workout in general.