This is done with a very simple bit of javascript - if you want to copy it and use it on your own page, just put this...

<script type="text/javascript" src="http://tupid.org/randr.js"></script>

... in the head section of your page, and this...

<span id="randrcountdown"></span>

... where you want it to appear. Or copy the randr.js file to your own site if you want to customize it.