I am trying to find page loading time of a page using following code

function loading_time() {


 echo '<p>Page loading time:'.timer_stop(0, 3).' seconds</p>';

}

 add_action( 'shutdown', 'loading_time' );

The code works perfectly for non cached pages but for cached pages the shutdown hook never fires.Is there any way to find out the page loading time of cached pages without firing the wordpress hook?