There are couple of ways to accomplish this:
1. Code your page like normal, then call it in a cron job via lynx* (you can also wget on the URL, or links -dump). For lynx, add the following to your crontab:
0 8 * * * /usr/bin/lynx -dump http://localhost/page.php >
/path/to/logfile/or/dev/null
Now, this means your script is in your public web space, so it could be called by anyone who knew the name of the page. You can put the page in a subdirectory and add an .htaccess file that restricts access to only 127.0.0.1 or you could code the script itself to retrieve the remote IP and make sure it was 127.0.0.1.
2. With PHP installed as a CGI you could also write your page as a shell script. As the first line of your script put the line:
#!<path to php> -q
Don't forget to set the executable bits. If you are running PHP as an Apache DSO, you can build php again without the with-apxs=/blah so it builds the binary executable and install it somewhere like /usr/local/bin. That way you can use php as a scripting language much like you use sh. With this method you can just call that script without relying on the webserver.
*lynx is a text only web browser