There is no fixed length, and that is intentional rather than an oversight.
When a sentence is suspended pending successful completion of a drug treatment program, the program is designed to run as long as the individual actually needs it rather than on a predetermined schedule. The clinical staff assess progress and make decisions based on genuine therapeutic milestones, not a calendar. Someone who engages deeply and does the real work may complete it in a different timeframe than someone resistant or going through the motions.
That last point is worth sitting with. A suspended 364-day sentence is a significant gift from the court, and the temptation for someone in this position is to treat the program as a box to check rather than an opportunity to actually change something. Too many people get through a treatment program by saying the right things, presenting the right attitude to staff, and walking out the door without having genuinely addressed what brought them there. The short-term win of early release becomes a longer-term loss when the same patterns reassert themselves on the outside and the next encounter with the system comes with far less leniency on the table.
Your role from the outside is to encourage the real work, not just the completion. Ask about what they are learning, not just how much longer it will take. The therapy is free, the time is already being served either way, and the window to do this with professional support and no distractions from the outside world does not stay open indefinitely.
This is the moment. Encourage them to use it fully.