I'd just listen to your body. Start with the lowest resistance setting on your elliptical, at a slow pace. Speed up or increase the resistance if you feel you can, and do maybe 20-30 minutes. If you feel OK at the end, and feel fine the next day, maybe up the resistance a little more, or go a bit longer. When you hit your "wall", you'll KNOW it! Work at that level until you feel you can go a bit more, then up it again.
It's no race, so be patient and pay attention to how your body feels.
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