Hi Leo,
I have been practicing Tai Chi for about 10 years now. I started doing very basic standing Chi Gung and some simple Tai Chi weight shifting exercises about one week after surgery, but no twisting movements. I started back doing the long form at about 7 weeks after surgery. Over the next few months I did get some subtle clicking during some of the twisting movements, as you suggested. At six months, that has gone away most days, though it does happen occasionally, which interestingly is usually associated with a less than perfect technical movement. My feeling from talking to the doctor, was that I should be careful with twisting movements for the first six weeks, which I did. After that, I feel that the slow focused movements of the hips in Tai Chi are ideal therapy, and has been a very positive aspect of my recovery.
John