As far as I know there is no danger in flushing more often than every two weeks. I flushed every week for a couple of months but since I only got stones out every other flush I changed my schedule to every two weeks. I have done about 25 flushes now and only half of them expelled stones. I will keep going until I am stone free for several flushes in a row.
There are potential benefits of waiting every two weeks or longer between flushes. If you liver is sluggish then it takes time for stones to move forward in the liver so flushing very frequently may not produce many stones. Also, a flush is like a natural surgery for your liver so waiting might let your liver recoup a bit.
In the end how often you flush should be determined by how you feel and the results you seek and obtain. No matter what your schedule - keep flushing until the liver and gallbladder are clean. The benefits are remarkable.