The practice's working hours are set globally in Settings > Sites. You must have the correct permissions to do this. Permissions are customisable by your admin users at the practice.

Click on the site, and then on the Calendar tab on the left-hand side to see the calendar options, including the opening hours of your practice.

Tick or untick each day, according to when the practice is open and click on the opening/closing times to alter as needed.

If a particular practitioner does not work your full practice opening hours, you will need to block the time they are not working using Recurring Appointments.

👉Take a look at this help article here on how to set up recurring appointments for your practitioners.