In the event that you require customers to be unable to book online, there are two possible options.
Option One -
Remove all online booking availability
This method will remove the ability for customers to book online. The process can manually be undone by reversing the method below.
Here you can un-tick the box beside 'Accept online bookings'
Be sure to scroll down to the bottom of the page and click Save
Option Two -
Create a periodic Close-Out
This method will remove the ability for customers to make bookings during a time period determined by you.
This option may be more beneficial as it will allow customers to make bookings in the future, for dates after the time period you close out.
This option also allows you to edit / shorten / extend / remove the close out at any time. Please see this guide.