You can run scripts in PHP at a specified time with the desired frequency. To do this you need to use a PHP-CLI interpreter.
Since not all PHP programs can run through the SAPI CLI without modification, you can run them through wget. For example:
/usr/local/bin/wget -O /dev/null -q http://mysite.tld/cron.php?action=123If the script uses require functions, include them, and they indicate the appropriate paths, to start executing the script, use the chdir() call function, which sets the current working directory.