Maybe the purpose of morning ES is to ensure that any stones which might still be moving down in the bile ducts won't get stuck? Or maybe it is simply for the general flush effect, to get all possible toxins out of the body the soonest.
I replaced the morning ES doses with a SWF (Salt-Water-Flush) as I feel it cleans me out quicker and less harshly. I have done flushes this way 10+ times and never had any problems.