Steps to create a countdown clock for your Blogspot blog:
1. Go to a site that let's you create a countdown clock and create your clock. Here's one such site: http://mycountdown.org/getwidget/
2. Copy the html code after creating your clock from the creation site.
3. Return to Blogger. Go to "Layout" and click on "Add A Gadget"
6. Congratulations! The clock should now be on your page.