Countdown clock

I need a very simple script showing a countdown. I need s clock showing a 24 hour countdown which it resets every 24 hours again. Basically it goes from 24h:00min to 23h:59 min and so on to 0h:0 min, then it starts again 24h:00min and so on. We need to be able to to set when clock resets, and so on. Actual format will be a fairly small banner: 1 Day Clearance Ends 24h:59 min