Need Help With Php GET function with timer

I need some help on creating a timer that every thirty minutes, refreshes on a URL. I know how to get the page, but I have no idea how to create a timer that initiates it.Could someone point me on a helpful direction?

this is the closest i got to finding what your looking for took about 3 pages worth of googling to find it but it should do the job. mind you i would get rid of the echo part since thats not needed at all.

<?php//  refresh / redirect to an internal web page//  ------------------------------------------header( 'refresh: 5; url=/webdsn/' );echo '<h1>You will be re-directed in 5 seconds...</h1>';//  refresh / redirect to an internal web page//  ------------------------------------------header( 'refresh: 3; url=/' ); # redirects to our homepageecho '<h1>You will be re-directed in 3 seconds...</h1>';//  refresh / redirect to an external web page//  ------------------------------------------header( 'refresh: 0; url=http://www.example.net );echo '<h1>You won\'t know what hit you!</h1>';?>

Hmm, I guess this would work, even if not the way I wanted it to. Thanks, I'm going to get to work now