How long does it take for benylin (dextromethorphan) medicine to kick in?

Depends. Benylin (dextromethorphan) is a group name for different formulations, i.e. Different ingredients. These different crug components are metabolized at different rates depending on many factors, such as age, fever, digestive status, nature of condition being treated. Generally some response should be noted within 30 to 60 minutes after ingestion.