It may well be me, but I am confused by the question and some of the answers ?. As far as I understand it, the bonus is £600 at the end of a 3 year lease and £900 at the end of a 5 year lease. You don’t get the bonus until the car is returned, whenever that might be. Obviously they can’t assess the condition before you have finished with it. If your new car turns up before your existing 3 year lease is up, you can’t pick up the new car until the end of your existing lease anyway, so as long as the car meets the criteria, your £600 will be sent after you return the car. If you agree to extend the lease to 5 years you still have the ability to order a new car at any time between years 3 and 5. You don’t have to keep it the full 5 years unless you want to. If you decide to order at such a time that your next car is available before your 5 years is up, my guess is that you can have it straight away but would get the £600 bonus rather than £900 as you haven’t gone the full 5 years but, as I say, that last comment is what I would think would happen whereas the other comments are factual. See link for more details;
https://www.motability.co.uk/your-lease/car/good-condition-bonus/