Custom Availability
You are able to edit and change your availability any time you wish. This can be for one-off unavailable days and times, if you are away from the office on vacation/holiday or any other reason.
To edit your availability for a specific event, simply:
1) hit Edit on your chosen Event Type / Calendar
2) scroll down to the Event Hosts section and check the Specific Custom Availability option
3) this will open up the Simple and Advanced calendar in addition to giving you the option to be date specific
4) from here, you are able to edit your availability just as you did when you first created your Default Availability
5) once done, be sure to hit Save & Exit for the event to be updated with your new availability