Hey, @Anzebukovsek .
Thank you for posting this question!
There are quite a few options for countdown timers, and they can be added to the cart page. However, if you’re looking to customize the checkout and add a countdown timer to the checkout, then it’s important to note that Customizable checkout is only available on Shopify Plus. That being said, here’s a few countdown timers that I’ve handpicked:
I noticed that you’re a Shopify Partner. I’d love to hear more about your experience so far and share some resources to help you get started!