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.

Hope this helps.

The doses of Epsom Salts taken after the flush potion at a time dependant upon the protocol adopted ensures the rapid transit of gallstones, stale bile and other potentially toxic debris through the intestines where it is evacuated without being re-absorbed. The terminal ileum is a part of the intestines just before the colon and is responsibly to reabsorbing 80 to 90 percent of the bile secreted by the liver and gallbladder. Venous blood from the ileum goes straight into the portal vein, and hence through the liver where the bile acids are extracted very efficiently and very little escapes the healthy liver into systemic circulation. The net effect of this enterohepatic recirculation is that each bile salt molecule is reused about 20 times, often two or three times during a single digestive phase. Liver Flushing combined with magnesium sulphate breaks this cycle by evacuating "stale" bile products before it can be reabsorbed and promote the manufacture of "fresh" bile.