A: You have not said what type of contract - GMS, PMS or APMS - the practice has.
There is no direct stipulation in GMS contracts for the number of surgery sessions offered per week nor, indeed, how long a session is.
There could be stipulations in a PMS or APMS contract but as these are locally negotiated, you will need to check the contract. There are usually conditions about surgery opening times in all GP contracts.
Also, the extended hours DES did require a declaration of appointments available to ensure practices offered more. The GMS terms of service requires offering reasonable services to patients at all times.