Click on the 'Availability' tab at the top of the page. Here you will see the options of Blackouts and Recurring Blackouts. If you are just looking to create a one off blackout for a certain day, you would choose the Blackout tab and click the green "Create New Blackout" button. Here you can choose which services, service areas, and crews will be unavailable during this Blackout. Set the date and time of this Blackout, and be sure to click on the "Create Blackout" button at the bottom of the page to save your Blackout. This is extremely helpful in situations where there are certain areas that you don't have enough staff to cover, or simply cannot make the commute due to heavy traffic on a Friday afternoon, etc. You can create a service area and black out service there for particular days/ times of the week!
If you are wanting to create a Blackout that occurs each week (ie: an early cutoff on bookings in a certain service area on Friday afternoons) you would choose the "Recurring Blackouts" option.