Your live service countdown timer is managed within an event, under Events > Events > Live Service.

Within the event settings, you can adjust the date and start/end times, which will controls when your service is "live" in the header area. You can also set for your event to repeat (ie: every Sunday), so that the timer will automatically start again after the "end" time.

You can have multiple "live service" events, but just make sure to assign the LIVE STREAM category. This will ensure that your event is synced with the timer, and it will then countdown to whatever event date is next that's assigned to the category.