It is possible to separate the visitors based on the followings:
How many pages have the visitor already checked on the site: this means that the popup displays for those visitors only visited at least particular number of subpages on your site.
From which site is the visitor trying to leave the site: If you want to make sure that the popup appears only on particular pages, you may use this setting (it is beneficial to use in case of i.e. for those visitors who may abandon your cart). Visitors who have not visited a page during the recent period of time: When there is a page on your site, containing useful information, but for some reason your visitors never check it, in this case you may use this filter.
Visitors who have been on the subpage for at least 'X' seconds: You may separate your visitors based on how much time have they spent on a subpage. Visitors who have spent at least 'X' seconds browsing the website: this feature is similar to previous one, but includes the entire website.