The countdown clock is a neat and clean way to communicate a "close date" of the store to your customers.
1) Within your store, click on Branding on the left-hand menu.
2) Open the Slide Content Tab.
3) Check off
4) Select
5) Select the desired close date you wish to display to your customer.
6) Select the time you want to display the store closes.
7) Select 
to save the changes.
The countdown clock is not connected to the store's true close date/time from the settings page. You can display to your customers the store closing on a Sunday night at midnight but the store can be set to close on the next day around the time you start to close stores on the Settings page. This helps to prevent the inevitable email in the early morning asking to have the store reopened for a last-minute order to be placed.