For a person wearing an ortho boot due to a broken ankle, how many months could it be before patient can begin to walk normally-minus the boot?

That depends upon how badly the ankle was damaged and how you respond to physical therapy. Post severely fractured ankles can be a chronic problem causing permanent ankle joint issues. Hopefully this won't be the case with you.

You should exit the boot when you are strong enough to protect your self from reinjuring yourself you have extensive WORK ahead of you. Rehab is work not fun.