*it's also worth mentioning, if you are going to be checked at any point, it would be time well spent to study the technical clarification guide (on the UCI's website) and be ready to plead your case when they fail you on something. Comm's are human and not always totally caught up on the game. I've had to argue with the -5/80cm twice (in both cases the comm was still trying to measure the athlete, around the time the rules were changed to no longer need that and to allow one exemption no matter what)
You may still get hit with having to make a change right before your start, but you at least have a chance if you've measured things yourself and know the rules. (I was helping an athlete for Pro Nat TT last year, her bike was small enough we could only just get it back far enough to be at 0 behind the bb, we moved her bars to 75cm, and at bike check we still had to plead that they let her start, as they measured it a couple of mm past 0 setback. There was literally no way for us to go further back besides a different saddle - which she didn't have - or hacking the nose of the saddle off. Fortunately they overlooked it)