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

On Linux/Unix (including Mac OSX), create a cron job.

# 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

30 3  *  *  *  wget your.domain.com/do_something.php

 http://stackoverflow.com/questions/1194857/how-to-schedule-the-execution-of-a-php-script-on-the-server-side