It depends on your setup.
Option 1: apply countdown per customer per session:
The countdown will work per customer per session.
For example, let's assume you set the countdown to be for 24h.
Visits the store on Sunday 4PM > see countdown -24h
Visits the store on Sunday 5PM > see countdown -23h
Visits the store on Monday 5PM > see countdown -24h
Visits the store on Monday 6PM > see countdown -23h
Meaning, the countdown is not per end date.
Option 2: Countdown to a specific end date
Choose a date and a time to start and end the countdown:
(!) The dates and times are in your local timezone.
(!!) You will not see the countdown if the start date did not arrive yet