If it's the course I think it is, it generally lasts for 14 sessions, once a week, and there is some pre- and post-group work that you do with your Probation Officer.
when you are convicted of driving with excess alcohol in either breath or blood you are normally offered a reduction in the length of time of the ban if you agree to attend and pay for a drink drivers course. Say the ban is for 12months the reduction would be for 3 months therefore the term of your ban would be 9months. The course must be completed 2 months prior to the end of ban. In this case 7 months after ban begins.