First select a knak template that contains a countdown timer. Sedona for example. Apply your options and sync the template to your Marketo instance.
You customize the date and color of your timer by using tokens in Marketo.
First, set up a text program token called countdown-date with your chosen date. You could write it as Jan 1, 2017 or YYYY-MM-DD like this: 2017-01-01. To specify a time you could enter 2017-01-01 00:00:00. Your date must be no more than 99 days in the future, and in UTC time.
Then set up a text program token called countdown-color for the color of your countdown text. The value should be a hex code without the hash. For example, white would simply be "FFFFFF".
Finally, set up a text program token called countdown-bg for the background color of your timer. The value should be a hex code without the hash. For example, black would simply be "000000".
If you are comfortable editing HTML, you may also find the two tokens listed above in the template code and replace them with your chosen values.
Please note that Outlook 2007, 2010, 2013 and 2016 do not support animation. In these email clients the correct countdown time will be displayed as a static image.