You should setup a cron task by yourself instead.
Just type crontab -e to edit the crontab and add the following to run your script every days at 11:00 AM :
00 11 * * * /path/to/script.sh
Or run your PHP script directly from crontab :
00 11 * * * /usr/bin/php /path/to/myphppage.php
Save and exit.
If you want to use an external script call (first sample i used with script.sh), you should specify full path to binaries/script within your shell script :
#!/bin/sh /usr/bin/php /path/to/myphppage.php
As a side note, using the appropriate shebang in your PHP script you don't even need to specify the program to use to run your script. Add the following at the beginning of your PHP file :
#!/usr/bin/php
Then your crontab will just look like this :
00 11 * * * /path/to/myphppage.php