How to schedule the execution of a PHP script on the server side?

If you're running a flavor of Linux/Unix (including Mac OSX), create a cron job.

If you're running Windows, create a scheduled task.

Note: both of the above links relate specifically to a PHP audience.

If you edit the crontab manually with crontab -e or go to list it with crontab -l, a useful comment to put at the top of the crontab is below.

# .---------------- minute (0 - 59) 
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ... 
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7)  OR sun,mon,tue,wed,thu,fri,sat 
# |  |  |  |  |
# *  *  *  *  *  command to be executed

  30 3  *  *  *  php /home/scripts/do_something.php