Some of the things that have caused problems in the past have been if you're using Netscape or another brand of Internet Browser other than the Microsoft Internet Explorer version 5.
Have you made a post of the countdown timer in the body of the post and not in the signature area? That is the only safe way to test your countdown timer so that it affects just that one post. When you put it in your signature area, it affects that post and also all of the posts you have made in the past plus the ones in the future.
If the post works and the counter is visible, it would prove that the code generator worked correctly for you. Then we can consider what could be wrong in the signature area or if it doesn't work, where else to look.
hope that helps