I'd do it early and get the complete kit done. If the belt goes, it's an £800 bill to sort out the mess, and they do go. With inflation and lack of interest you'll be getting on sticking the money into a savings account, it'll just cost more to do next year anyway. The only exception would be if you want to get rid of the car in which case do it now. I found that in general 72k services were very often expensive as they needed a belt and bigger service and very often tyres and brakes and suspension components at the same time on that service, many a "cheap" 70k car that "just needed a service" turned out to be a bit of a wallet buster for a new owner.