I need a simple repeating Countdown

Your plugin is great. I need a simple countdown.
00 hours 45minutes xxseconds
When a visitor lands on the site, I need the countdown to begin on the number of minute I designate and countdown to 00. I don’t have an event date. I never want my countdown to stop working.
How do I set this up. I have read every thing and cannot get it to work the way I need it to work.

Please advise.

Thank you in advance.