Answer is that if you are a low mileage user, it has to be done within 30 days of the date registered. If you are doing the servicing on the mileage scale as you are, you have to have the car serviced within 750 miles of the due service. So as long as you dont go over 13,250 you are ok if you exceed this you invalidate your warranty. The comment above about the car being booked in is not correct. It is when the car is in the workshop, technician working on it. If it was the other way you could have a courier vehicle booked in and in the week that it is booked it could have done another 3,000 miles by the time it comes in. Hope this helps, but if you want to double check then ring Citroen UK on 0870 606 9000 which is the main number they will tell you exactly, but I do think I am correct.