Running a PHP script after a time-lapse is a function of your operating system. In 'nix it is bleeding easy to set this up. Checkout crontab (man crontab) and once you get a handle on the syntax, you are good to go. Add a task to be run on Mondays which runs your script.
Here's an entry I have in my crontab which runs a script named "growth.php" every twenty minutes and passes it the switch "-a":
0,20,40 /home/uro/html/.scripts/growth.php -a 1>/dev/null
If you have the (mis)fortune of being in Windows, you get to use the Windows Scheduler. I am not sure how to even run a script in Windows, but there's got to be a way.