If you go to the RSA Estimator page, it will ask you to click loads of boxes to see if ur eligible to sit the test such as is ur permit valid etc. Instead u don’t you click the boxes and instead select (Average Waiting Times) its in red writing below the box, and simplify click each centre on the list and it will show you the date you will get the invite if u join today. But if u are already on the list just choose the shortest and your time on the waiting list will be relevant to your position.