Your business hours determine which hours customers can place an order from you. Note that hours must be set in Square Dashboard, not Square Online for your app.
You set your business hours in Square Dashboard.
You can also find the steps under Manage Multiple Locations with Square.
Once you login, head to Account & Settings -> Locations -> select the location you wish to adjust.
On this page if you scroll down you will see the option to edit your business hours.
In Orda Dashboard -> Locations, uncheck the location to disable it. Make sure you enable it again when the store reopens.