Although Klonopin starts working within the first hour after ingestion, according to the manufacturer, it takes about 1 to 4 hours for peak concentration in the blood to be reached. And it takes about 30 to 40 hours for the system to break down 50% (half-life) of the active ingredient (clonazepam) Klonopin is initially more potent than Valium (diazepam) but may last a shorter amount of time.