As with learning any new skill, the effects are cumulative.
Most people experience improvements after the first few sessions; however they will likely only last a day or two. After more training and further reinforcement, the changes will last longer.
As the psychological core improves, old habits naturally shift into healthier ones. Like building a muscle, strengthening new neural-pathways requires some practice.
Based on our more complex equipment, most clients notice their first changes within the first four to six sessions, however a minimum of a dozen sessions are recommended to ensure that the changes hold. On more simple equipment, it will take longer.