The length to time in treatment , whether it was an adult or child, would be a direct corralate of how much movment that needs to take place to satisfy your treatment goals.
I've done some cases in a few months and some have taken years. It really just depends on the complexity of treatment. That said, adult treatment often is shorter than children because we do not try to correct skeletal problem (the patient is not growing) and the patients tend to be more cooperative