I've had full knee reconstructions on both knees (don't ask). Post surgery, I was told that it would take upwards of 6 months to heal as long as I followed the courses of physio treatments and exercises I was given. Luckily for me, I healed quicker than expected (4 months) and much of it was due to the stationary bike at the physio. Biking can actually be good for the knee as it gets a good workout without the impact that you get from running. I can still ski (although it took 4 years after the surgery to work up the courage, even though I was told by my surgeon that I could go back after 18 months), dance and do pretty much anything I want now, but I won't run on them at all. When I do run (touch football occasionally), I really feel it the next day - pain and swelling.

Essentially, don't skimp on the physio treatments and exercises you are give. Do all that is asked of you without fail and you should be able to come back as good as ever. Also, if there is pain, STOP - doing any more damage is not worth it in the long run.