Do I have to put the registration straight onto a vehicle?
No. You have until the expiry date shown on your V750 to put the mark onto a vehicle.
If you are still not ready to put your registration mark onto your vehicle before the expiry date printed on your certificate of entitlement, then you can extend the entitlement period for a further one year, two years or three years for a fee of £25 per year. You can apply online via "My Account" for 1 year or sign section 2 of the certificate of entitlement and send your application and cheque made payable to DVLA at DVLA Personalised Registrations, Swansea, SA99 1DN. Your application must be made before the certificate expires but only within 28 days of the expiry date.
There is no limit to the number of times you can extend the entitlement period.