I need a program that I can run that allows a potential client to enter/browse my membership site for a specific time (like 30 min. or so)for free, and then a pop up will shut down access to the site and present my offer to them to subscribe to my site so they can decide to continue accessing my membership site on the spot.

For example....someone goes to my site after seeing an ad....they can enter my membership site for free after they enter their name and email, and then after 15 minutes, the site closes and a pop up shows up and presents an offer to sign up for a monthly membership subscription.**I am not finished with the membership site yet. I am thinking ahead, and want to have this program ready to go once my site is up and running.

thanks,
Scott