That's something that I had left out of the "DKPSystem.com" layout, but that you could insert into it if you wanted (it's a standard feature on the other layouts).
It's a matter of inserting the <!--System:Countdown--> command into the layout.html file, in Admin > Advanced Layout Options.
Let me know if you need further help with that.
If you could give me more of a step/by/step on where exactly in Advanced Layout Options to do this (we talking the CSS editor?) I'd appreciate it Chops.
layout.html
Admin > Advanced Layout Options
You'll have to download your current layout.html and edit to place the system tag Chops referenced in it. You will need to find a table in the file suitable to hold the countdown or alter the file slight to place a table on the page to hold it. Typically this would go in the main content are of the page above the title.