You can build in schedules for holidays and there is help and support available in the Block Visibility Knowledge Base.  However, editors find it easier to manually disable the day of the holiday from the day of week controls instead. 

I like to switch on the page list view to see all the blocks on the page to be able to select the correct block for editing (this is an icon at top left of the editing screen).

Usually the block visibility control is applied to a group containing one or more blocks. So select the group to bring up the block controls on the right side of the page editor.

Change the repeating schedule

Example: Hide the block on a Monday bank holiday
On the week before a Monday bank holiday deselect the day 'M' from the block control. Then after the holiday enable the day on the block controls.

NOTE: Don't forget to switch the day back on again again after the holiday has taken place or that day will be off forever.

Override schedule to hide block e.g. if you have reached capacity for the day

If you want to temporarily hide the block you can switch on the 'Hide block from everyone' control, which overrides all schedules and disables the block. You may find this handy for times when the surgery is overwhelmed with requests and you want to temporarily disable the form. 

NOTE: Remember to deselect this option to return to the regular schedule or the form will be off forever

If this option is not showing in the visibility controls you can activate it by selecting from the visibility control options: