if you can get root / ssh access, you can set yourself up a cron job.... now im lazy, so iv only ever used admin panels such as plesk and webmin to set up cron jobs, so i dont know how to do it off the command line....
once you figure out how to actually add a command to the cron list, the actual command to run the script will be something like
php /direct/path/to/your/script.php