Show popup for first time users on my site

I'm wondering if there is a way to show a pop up for my users who are registering and logging in for the first time, and then never again afterwards. Basically I'm using Pop Up! for welcoming new members to the site. I've gone over the settings but I'm not seeing an easy way to pull this off. The closest thing I could find was the setting that says "Popover shown less than" but the wording is a tad confusing. I set it to 1, and the popup never actually appears upon logging in the first time. Any advice?