The exercise is only meant to be done when you feel you are able to do it.
Can you walk 2-5 hours/week? It can be done all at once or spaced out over the week.
Even if you can do that (the minimum, or less, even) you will benefit from some exercise. Your body will heal and you will have more and more energy as time passes. You'll get there eventually. It's a continuous healing process.
Best of luck and stick around so we can help whenever you need it.