Our ped endo explained that for children, the larger dose is given at the end of the day to help suppress the ACTH surge that happens usually around 3 am. This way, the extra cortisone also helps suppress the extra progesterone otherwise produced. I specifically questioned the ped endo(who is 2 hours away) on this after my daughter was in our local hospital and a regular endo treated her. The regular endo mainly deals with adults and he argued with me about the way the dose was given - the larger amount was in the evening. The ped endo further explained that particularly adults with Addisons need the larger dose in the AM.