No, don’t worry - if they said that is when they want the test to be done, that’s fine. Perhaps they are confident that the appointment with the surgeon will happen around week 6.
The Gleason score tells them how seriously to take the cancer. Generally a 6 doesn’t spread quickly but a 7 is more developed. They can tell whether the cancer had escaped the prostate by looking at it in a lab after the op - they can see if there are cancer cells on the outside or whether they are all contained inside. The results from the lab and the PSA test they will do next week will tell them whether the op has been successful.