U.S. Department of Health and Human Services says that losing a lot of weight may need up to 300 minutes of exercise each week. If you are only using your elliptical for this, that equates to five hours. You can supplement this with walks and other exercise, though. Don’t do it all in one go. Five one-hour sessions might be a good way to lose weight. If you find this too difficult to start with then you can start with 30 minute sessions and build up to it. Don’t go with high resistance to start, as this will lead to a lot of aches and pains.