Unix 'at' command via PHP to run single function
Sure, you can use at or cron, and pass the -R flag to PHP to execute the command line:
# Run phpinfo() at 12:30...echo php -R 'phpinfo();' | at 12:30Or it is perhaps better to call a file which may contain multiple commands
echo 'php /path/to/yourfile.php' | at 12:30
To do that a PHP script would need to be persistent inside the PHP interpreter for some long interval of time.
The best you could do would be to use something like exec to create the unix command you's use and then call the php command line version to make it work. Look at Scheduling php scripts for more information.