I just thought I would add my personal experience to this thread for what it's worth.
Long before I ever tried a Liver Flush or even knew what it was, my natural doctor advised me to do coffee enemas. After doing these coffee enemas, I felt/heard a gurgling from my gall bladder area and wound up passing several greenish stones the size of marbles that looked exactly like most of the Liver Flush photos people post here.
A year or so later, when I found out about the liver flush, I tried it and passed many more stones identical to the coffee enema ones. My first thought also was that perhaps these stones formed overnight as a result of the olive oil mixture, but while examining the stones I found them very hard, dense, and when I squeezed them with a chopstick, the inside was so dense and sticky that I had to scrub the chopstick with detergent to get the stone residue off. To me the stones had the appearance of something that had been formed slowly over time, as I can't imagine something that hard and dense being formed in just eight hours in my intestines.
There you have it. Hope this helps someone's questions.