How long it takes for symptom relief varies with the problem. In any event, I can always promise patients that within 10 or 15 sessions they will see some change. Maybe not a cure, but a clear difference in how they think, feel, and act, or in how things look to them. This has actually become a rather conservative estimate.
Many patients see a change sooner, sometimes a big change.
Other kinds of problems need more time. In general, those that are less circumscribed take longer. That is, something which is part of a general pattern of troublesome behavior and feelings in your life probably won't evaporate as quickly. This should make some intuitive sense. A behavior that is more embedded in your personality, that reflects your overall way of getting through life, will be more difficult to uproot than one that feels like a thorn in your otherwise comfortable side.