This article shows how you can edit the hours that a practitioner is available.
You can edit your clinic's opening and closing hours in the Business Setup menu option. This defines the clinic's hours as a whole (Business Setup -> Diary Settings), but practitioners have a separate configurable weekly schedule in the Employees section of the program.
Select the Employees option.
The employees screen will appear, similar to below:
Locate the practitioner user and click on the View button to look at their details. Scroll down to their Employee Schedule section.
Click on the Save button to apply the changes.
Within you Diary, you can still manually book in appointments during the greyed out times for a practitioner. They are just there as a guide, primarily for reception staff. The only time they are enforced is through front end online booking.
If you wish to open up a specific day as a once off for a practitioner, you will still need to open this day from the Diary, and then create a recurring block for the couple of months after that. Then, when you no longer want to have that day open, you can just go back and toggle it off and then delete your recurring block.