When you create a 'single booking' service, you can allow bookings to be made during any available hours, however, there may be times that you want to prevent bookings to be made.
Even if you have selected "during any available hours", you can easily block out specific time periods to prevent customers from making online bookings in the 'Availability' section of the service setup.
Setup > Services > Availability
Using the 'Block-Out Times' feature, click and drag across the time-slots to prevent bookings at those times.
To release the blocked-out time, simply click on the block-out section again.