If you have been doing Liver Flushes for 15 years then I guess you are an expert yourself. You asked 4 specific questions:
1) Did the slow reaction to ES affect the flush?
No. Your stomach will have been empty because you have fasted since 14.00hrs. The flush potion will have worked just as it is supposed to.
2) Should I get clear diarrhoea before taking the OO+Grapefruit?
Epsom Salts is officially reported as acting within a time of 1-6 hours, however other sources report 3 to 12 hours or even longer up to 24 hours. Many people report that the watery diarrhoea occurs mid morning of the second day which is approximately 14 hrs after the first dose. I assume it is dependant upon the transit time through the small intestines. Epsom Salts not only purges the stomach; it also contracts the gallbladder, relaxes the sphincter of Oddi (Increasing bile flow), and increases gastric, intestinal and pancreatic secretion.
3) Does this have any effect on getting or not stones and chaff?
The Liver Flush is more than counting stones. The process expels bile and prevents it from being re-absorbed in the intestines and recirculated through the liver. This forces the liver to make "fresh" bile. Bile attaches itself to toxins and drugs and maintenance flushes is thought to stop these unwanted chemicals building up in the liver.
4) What can I do to beforehand to bring my body to react to the ES quicker so I can start the flush with a clear intestine?
Nothing, if you follow the protocol and get watery diarrhoea you are doing fine and must be congratulated on havening a "clean" biliary system.