Adult Video Script Modification PHP Emailing New Users

I am running a PHP Script called Adult Video Script. I need the script to send a private message to a newly registered user in a random time frame of 5-20 hours after sign up. The private messages need to come from a specific list of users (random) that I have created on the website. I have about 10-15 "private messages" that are ready to be sent to the new users. I also need the system to e-mail the user to let them know they have received a private message, and a link in the e-mail so that they can jump right to the private message and respond. When a user responds to the fake users I have created, I need to get e-mailed showing that they did respond. All of the fake users have the exact same e-mail address so this shouldn't be too hard. If any of this is confusing please send me a private message with questions and I will do my best to answer them!