This is an LCM related problem
Finding the LCM of 40, 60 and 72
60 seconds = 1 min
360 min = 6 min
LCM (40, 60, 72) = 2 × 2 × 3 × 5 × 2 × 3 = 360
After 360 seconds they will change again i.e after six minutes they will change again i.e at 8.06 am they will change again simultaneously.