Klonopin typically starts to produce a calming effect within 1 to 4 hours after taking it, and the effects can last for up to 12 hours, which is longer than some other benzodiazepines.
It has a long half-life of 30 to 40 hours, meaning half of it will last in the body for that length of time. It usually takes 5 half-lives, or 6 to 9 days for Klonopin to be completely out of the body.