The Futurama email template offers space for a countdown timer, but the numbers are rich text only. How can I manipulate these rich text fields to show a real event countdown? 2017-06-12_1355
Sendtric's pretty good for this purpose. There's a few other folks who do this as well, but they start to charge at a much lower threshold.
This layout is assuming that you're making the counter yourself via PHP or something similar (which is quite odd, considering folks who know to do that...also would be making their own template.) Nearly every product on the market just sets up their timer to be one giant dynamic image, so you'd just do a standard image placement in your email template.