I've made a countdown widget. You can download it here: http://silverstripe.com/widgets

Some testing and feedback is still needed, but it should work.
There are five event types you can choose. The widget will automatically detect/generate a pattern, so this is a one time configuration thing. Just enter in the first occurrence of an event, and you’re set. To make it timezone independent, you do have to make sure the date and time is in the same timezone as your server’s time.