From the Air Cadets web site:
Most of our volunteers have busy lives too, and many of them work full time. Most activities take place in the evenings and at weekends, and no-one's expected to take part in everything. Many people get involved initially because their children are cadets - they start off helping out informally at events and open days. As long as you can spare a few hours a week, you'll be made very welcome.
Air Cadets - Join as a Civilian Instructor