Heartma sensory did this experiment where people came and then he was collecting plasma, I'm not sure whether plasma or saliva, melatonin samples every one hour. He found that around two to three hours before these people went to bed, that melatonin began to rise. But after they wake up, even if there was bright light, it took almost two to four hours, in some cases, four hours for the melatonin levels to drop by at least two hours.