Originally Posted by CaptainHank

I think the frequency parameter will solve this for you. From the Get Code > Popunder, check the "More Options" options from below the code and set the "Fire every [ ] page load(s)" to a high number (e.g.: 99999). The cookie expires in 24 hours, so you should get the desired behavior.

Let me know if it works as expected. If not, I can implement something different that will fit your need better.