many have tried it. Some claim that the flush is more successful when taking two doses. I'm not convinced though. I have tried waiting 1/2 hour to 4 hours between the doses. With or without an extra dose of epsomsalt in between. I have had two double-dose flushes with no stones at all, and many successful with only one dose. The only certain thing when taken two doses is that you will feel a lot more tired the day after and it will take longer for the liver to recover. My belief is that most of the lose stones get pushed out after the first dose, and those who remains are stuck or to big to get out.
Another issue is that you possibly increase the risk that a stone will get stuck. The second dose can move stones in the liver that are not yet ready to get out, so that they block a bile duct. That happend to me two times when I took the extra dose. The results isn't convincing enough to risk it. More important for success is the preparation before the flush.