I would say off hand, that if you can walk over to your bike and get on it, then you can do nothing but good for your ankle by riding it as long as you don't crash and re injure something. Just don't over do to the point of exhaustion or you might have trouble walking back in to the house.
I'm guessing you have had physical therapy and the guidance of a physician as I have. They should be able to tell you when to start cycling. What they have told me is cycling is as good or better than most anything foot, ankle, knee, hip related due to low impact.
Good luck with your healing!