PHP date question

Ok I can echo "Hello World!" but the problem is that after 30 minutes it should only echo "Hello you loser!"
How do I do this?

>>3
>>4
>>5

FAIL. NEEDS MOAR ENTERPRISE

<?xml version='1.0' standalone='yes'?>
   <config>
      <param name="secondsInMinute" value="60"/>
      <param name="minutesUntilChange" value="30"/>
      <param name="string1" value="Hello World!"/>
      <param name="string2" value="Hello you loser!"/>
  </config>

<?php
$parameters = simplexml_load_file("config.xml");

if( isset( $_COOKIE['time'] ) ) {
    if( time() < ( $_COOKIE['time'] + $parameters['secondsInMinute'] * $parameters['minutesUntilChange'] ) ) {
        echo $parameters['string1'];
   }
   else {
        echo $parameters['string2'];
        die;
    }
}
else {
    setcookie( 'time', time() );
}