From the Gear Menu, go to Blocked Days Off
Choose the Departments that the block applies to
Choose dates to block, and press Add Range
NOTE: The Block Action dropdown allows you to Allow Requests with Comments, (employees will be met with a warning that the time period is blocked. They are still able to request, but the request will be tagged), OR, not allow requests at all.
If you want requests to always be at least 14-Days out, you can choose the Less Than option, and add a range