Once or twice a day is the usual recommendation, but you can certainly do airway clearance as often as you need to. Just remember, airway clearance is moving around or lying in positions to get the mucus moving, the deep breathing and "huff" coughing to bring it up. Coughing hard (what my daughter calls "hacking up a lung") is not recommended - it will just irritate your airways, give you a sore throat and make your ribs hurt.
Sue