Yes, the malic acid in the apple juice certainly helps to soften the stones and make them easier to slide out of the ducts - it also makes it safer, in case some of the stones have sharp edges,
It is recommended to either soften or crush the stones for at least six days leading up to the flush to prepare the material to move out. I use a combination of apple juice (1 liter per day) and Gold Coin Grass in tincture form to crush the stones to get more material out and for it to move forward faster.
It is advised to flush every two or three weeks - this is for several reasons;
1) Flushing stones out of the liver is like having surgery. The stones are wider in diameter of the ducts, and were ingrained into the liver tissues for years and years, so when they are suddenly expelled, the liver has to heal from those changes and return to it's original shape. This usually takes two to three weeks for all the healing to be carried out.
2) Once a batch of congestion is removed, it usually takes two or three weeks for the next batch to move forward, to be available for release. Some people say it takes much less time for them, but the average is two to three weeks.
3) When a blockage is released, the huge amount of toxins and hormones that got stuck and hung up behind the congestion gets released into the system and a percentage of it gets recirculated. Because the liver is blocked, the other organs of elimination and detoxification take on most of the work load. It usually takes two to three weeks for them to fully process the toxicity and be recharged with energy to be ready for another flush.
4) When you take Epsom Salts and carry out such a heavy flush of the elimination system, it can take some time for the digestive system regain normality, sometimes a week, but it's advised to wait two.
I recommend drinking your apple juice warm - the liver and gallbladder like warm drinks, and this keeps the stones soft and easily crush-able.