Ads with countdown timers are considered customized ads in Google Adwords, as opposed to the standard ads that have just text. Ads with countdown timers are useful to drive a sense of urgency to the viewer, saying that time’s running out to take advantage of a promotion you’re having: Hurry, sale ends in X days!

An example to use the countdown timer is:
“This sale ends in {=COUNTDOWN(“2016/06/26 09:00:00″)}!”
which would result in
“This sale ends in 3 days!”

More info can be found here.

We were very excited when we tried it. What we didn’t know when we started was that customized ads have to be served with at least one standard ad alongside it. Because we didn’t [server at least one standard ad], our customized ad with the countdown timer WAS NOT SERVED even though the ad was approved. We only realised something was wrong after the sale was over when we checked our numbers.

Therefore, please do do do remember to serve at least one standard ad alongside customized ads for them to be served. Ads being approved DOES NOT mean it’ll be served. Lesson learned. Hope reading this post saved you some painful learning time.