How long on average will it take to cure depression?

That is variable: Every person is different. A major factor is the person. Do they take any prescribed medications consistently? Are they aggressively involved in talking therapy? Do they work to get at least 8 hours of sleep per night, healthy diet & daily exercise? Is the person really willing to examine their issues (even if painful)? Is this chronic depression or recurrent depression? There are many factors.

DEPRESSION: The most responsible answer I can give you is that it depends on the patient; it takes as long as it takes and everyone is different. And that's OK.

Depends: Symptom of depression can generally be controlled over a few months, however, the propensity to depression may be life long. It is imperative to seek competent care from a psychiatrist and follow advice about medication and psychotherapy. Regular exercise will help in controlling the disease. Wish you good health