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 youÃ¢â‚¬â„¢re set. To make it timezone independent, you do have to make sure the date and time is in the same timezone as your serverÃ¢â‚¬â„¢s time.