Many people ask me how much time do they need to exercise every other day in order to lose weight! Well, the answer in the weight loss factor is total number of calories you consume vs the number of calories you burn.
I suggest working as hard as is comfortable without risking injury. This will get you as aerobically fit as possible, and being as fit as you can has advantages for weight loss because you probably will be able to do more activity (exercise and activities of daily living), and that will contribute to how many calories you burn all day. But keep in mind that no matter how many calories you burn with exercise you still will not lose weight if you consume more calories than you burn. If you burn 2000 calories all day with exercise and all other activities, but you consume 2500, you won't lose weight. And keep resistance exercise like weightlifting in mind since it helps you build muscle, and muscle helps set your metabolic rate, so you want as much muscle as possible!