The new calendar has the "block" functionality, to prevent bookings from being made at certain times that a resource might be unavailable.
1. How to block time
Click on the calendar at the required time and select 'block time' from the drop down.
You can name the blocked time in the title box, and set the start and end time.
Click 'block' to save the time block. It can then be dragged around the calendar if it needs to be changed at any point, or you can click on the time block and use the 'edit' icon to change it.