Urine samples were collected on all four days of the experiment at three time points: 21:00, 23:00 and at wake time. All urine samples were frozen (-20OC) immediately after collection. Melatonin was then analyses and secretion parameters were estimated. As the first morning sample concentration of 6-SMT has been extensively used as an estimate of overnight melatonin secretion (McMullan et al., 2013), we used this sample to represent the maximum (100%) MLT secretion per participant. The night samples (at 21:00 and 23:00) were transformed using the formula value at 21:00 or 23:00 /value in wake time *100 to reflect the percentage change in MLT secretion per participant.