Tumors can grow rapidly, but I suspect that the tumors were already there, although probably smaller. "Good medical practice" suggests that the initial TURB be repeated a few weeks later for this very reason. The first time the urologist looks into the bladder, he may not get a really good look....the second time they know a bit better where the problem areas are and can get better samples.
In my case, I was diagnosed with papillary after the first TURB, with several areas that were somewhat questionable. The second time, a few weeks later, the urologist concentrated on the areas that were questionable, and found CIS.
Sara Anne