If anyone could predict that…well, now THAT would be amazing.  Because of the billions of possibilities that factor in and exist between humans and their ailments, it would be irresponsible to give a definite answer.
In many seemingly difficult cases that mirror each other very precisely, some took only 2-3 sessions, and some others 10 sessions. Generally, using most other natural or alternative methods it takes one month or treatment for every year that you have had the condition for the treatment to do any good at all. In nearly every case, Bowen works MUCH faster than this, usually only 3-5 sessions, generally 7 days apart, (in very rare cases more frequent sessions have been found to be very useful) will be all that is necessary to bring the body back into balance for most people.  With Bowen it is very common for people to heal in about 35% of the time it would normally take, especially after a surgery or major trauma.
Again, most conditions respond very rapidly to 3-5 sessions.
A more serious or chronic condition may take several sessions to begin seeing results and even longer to help the problem resolve. Some conditions are so long-term, extreme and complicated by age or other factors that a complete recovery will not happen. In these cases, ongoing treatment at regularly scheduled intervals is the what is needed.