Sessions are tailored to you and the role the habit plays in your life. Some patterns change quickly. Others need a few sessions to unwind the layers underneath. Either way, you stay in control the whole time as hypnotherapy is a focused, collaborative state, not something done to you.
A note on dependence: if you are managing substance dependence, hypnotherapy works best alongside the care of your GP or treatment team. It is a strong support, not a replacement for medical care.