Many different options and formats are available.

Configure your countdown.

Be Sure to select 'Secure web page...'

Copy the resultant HTML

<iframe src="" allowTransparency="true" frameborder="0" width="278" height="69"></iframe>

Use the embed edit function, select "Code" and insert the text you copied. Note that if you use Google Chrome you may find it impossible to resize the height of text box. If possible use Firefox for this purpose. See This.

Alternatively you can insert just the URL, such as:

You can drag the result into the header if you wish.

You can insert it into the custom footer also. Example: