Try this 
:
User CP
Under Settings & Options
Edit Signature
Then insert into your signature box using your own dates
HTML Code:
Next Aruba trip in [countdown=12/31/2010 5:00 AM;I'm finally there]Count down:[/countdown]
You can view all of the code above by using the scroll bar.
When you have your code inserted into your signature, make sure scroll down and click "save signature".