You want to have a pop-up display once every 24 hours to visitors of your site.E.g. On Monday visitors would see Monday's pop-up, on Tuesday it would be Tuesday's pop-up etc.
Is this correct?
No, it not.I want to have a pop-under display once every 24 hours to visitors of your site and only once pop-under url. On monday ,tuesday ...... see same pop-under.Pop-under not pop-up please!
I still not quite sure what you're asking, but here's a great tutorial on how to create user friendly pop-under ads: http://icant.co.uk/articles/how-to-create-popunders/
As to deciding how to display this, maybe you could set a cookie which expires after 24hrs and serve the ad based on its presence/absence?