You can have as many different schedules in FlexBooker as desired, and each employee can even have multiple schedules.
Each schedule can be set with both a start, and optionally an end date.
If there are any days that two schedules for the same employee intersects, then don't worry, the system won't allow double-bookings, it will just allow booking for any hours that there is availability in either schedule.
So, let's say we want to open up two extra days during the week of Christmas only:
Under "Set Up" page > "Schedules" label, click on "Add New Schedule" and choose Flexible Time, you will be allowed to Set the time frames to a fixed time and date (beside the recurring weekly label):
2) You will then be allowed to add multiple appointment dates where you are allowed to add your specific schedule for a certain date:
3) You can set buffer time and add service/s for this schedule.
Click on the "Save" button to save any changes made, and now those days or hours will now be opened up!