The question of "how long to treat a patient" is a complex one and I think, can be looked from a couple of directions.
First of all is the question of prognosis regarding the resolution of the symptom you are focusing on primarily. This is probably your patient's priority and is also what your treatment is centered upon. Although the general "recommended" course of treatments is approximately 6-10x, this is of course highly dependent on factors such as patient compliance & overall health, severity & chronicity of the problem as well as your abilities in choosing a point/herbal rx and then performing the treatment. Generally what I see in my practice is that after 3 treatments, I will be able to gauge with much better acuracy how many treatments I think a particular patient will need to resolve a particular problem. The ability to make this judgement can only come with clinical experience. I always talk to my patients about how all the factors mentioned above play a role in recovery so that they can understand how I am looking at the problem.
Another important perspective in the question of how long to treat a patient really highlights the difference between a holistic approach to healing vs. simply focusing on resolving a particular illness. "Health" is a vague term which we think we understand and yet it is difficult to get everyone to agree on exactly how to measure or describe this state. OM fundamentally understands this concept since it has built into it's theory the concept of relativity. We look for evidence that a patient is moving in a positive direction both in regards to the symptom and to the overall state of health. Alopathic medicine often restricts the evaluation to changes in the complaint only and once the "symptoms" are gone, the job is considered done, even when a patient is clearly not "healthy".
When a patient has other underlying patterns of disharmony in addition to a particular symptom (e.g., digestive weakness in addition to the frozen shoulder that s/he wants treated), then resolving the symptom does not necessarily help her to be "healthy" in the broader sense. Thus, the recommended course of treatment for the patient may be much longer if the underlying goal is to improve her state of health.
A holistic practitioner who hopes to improve a patient's overall "health" is juggling both treatment for symptoms and treatment for overall harmony. I think that one of the most important roles we play is to educate our patients so that they better understand themselves, their bodies and what the concept of "health" means for them. In this way, the question of "how long to treat" will really be based on the goal set by the patient herself. How far a patient wants to move toward "health" is really a very personal decision, especially once a nagging or severe symptom is resolved.
You can be flexible and supportive as a practitioner and then watch with amazement the beautiful process of another human being evolving into a state which is stronger, healthier and ultimately happier.