This code snippet is perfect for showing popup to users after an exact amount of time, and will only show once because of it's time out setting. Scroll up and click on the demo link to see how code is working in real world, clone the project and modify however you want. You can also check how code was added to page.
On line 3, set the amount of time before cookie time out. Currently it's set to 30 days (in miliseconds). On line 4, set the delay before your popup or other element appears - it's also set in miliseconds and currently set to 10 seconds.
Copy before tag:
<p> CODE: https://gist.github.com/martinhudobivnik/ba7f0c475693b8325ed3c65d66f9245c.js</p>