Aim for at least 30 minutes of moderate-intensity or 15 minutes of vigorous intensity per day for health benefits. Suppose 15 minutes a day on the elliptical is all the time you have. In that case, the American Council on Exercise recommends you use that time as efficiently as possible by doing High-Intensity Interval Training (HIIT), which is a departure from the 30 to 60 minutes of continuous steady-state cardio that most people do on cardio machines. When you train at a higher intensity, even for a short time, you burn calories more efficiently.