Cortisol has a role to play in our biological clocks or the diurnal rhythm of our bodies. Our biological clock is responsible for telling us when to go to sleep and when to open our eyes and wake up. If you have healthy levels of cortisol, the largest dose of it is released in the morning. If an individual has Cushing's disease, the highest release of cortisol is at night. Also, levels are constantly changing and differing depending on the time of the day, so cortisol saliva tests can be performed several times throughout the day. The test procedure involves swabbing the mouth with cotton swab and letting it stay there for a couple of minutes until it is saturated, after what the swab with the saliva specimen is placed in a test tube.