As long as they are healthy, you could wait a while longer. If you start seeing a fair number of yellow leaves at the bottom of the plant, which is normal around harvest time, you know the plant is sending you signals that it ain't gonna produce anymore. Don't forget too, proper drying and curing also promotes a better flavor/taste and effect, kind of like ageing spirits...the longer they age the smoother the get like 25 year old Scotch whiskey or Romulan ale!