Yes, the sand like particles are coming from your gallbladder. It's grit and stuff--very common--nothing to worry about. Every Liver Flush you do will be different, so never expect your next one to be like your last one. My 3rd flush produced the biggest and oldest looking stones. I kept on flushing until I saw no more stones. How long you wait is up to you. The reason Dr. Clark says to wait 2-3 weeks is to give the stones that were pushed to the back time to move forward.
But, congratulations on taking that big step toward a healthier body!