If you need to prevent bookings at certain times of the day, you can quickly add a 'busy time' for any duration of time.
If your business has multiple staff and/or resources, you must ensure you are in the individual view to add a busy time. In the 'Diary' you can select the individual staff or resource from the sidebar. If you can not view the staff/resources in the sidebar, click on the arrow as indicated below.
To add the busy time select the time-slot that you would like to prevent bookings from.
This will open the 'Add new' window where you will be able to select 'busy time'.
The duration of time can not be changed on this screen so simply press the green 'Add busy time' button. Return to the selected time-slot and hover your mouse over the two lines highlighted below. At this time your mouse icon will change to arrow allowing you to click and drag down for the duration of time required.
Please note: If you have multiple staff and/or resources and would like to prevent all bookings for a period of time during the day, you will need to add the busy time to all available staff and/or resources.