Allow Patchs request limit / demand management blocks to be in 30 minute increments

As a Patchs GP practice admin user
When editing the demand management / request limit slots for my practice
I would like to be able to set them in 30 minute increments
In order to give me greater flexibility in setting demand
Such as allowing me to set demand for the first 30 minutes between Patchs being opened and our phone lines being opened