PHP sleep () not working

I am making a php file that will fire an event in five minutes. From the documents, it seems that only five minutes will be required to wait sleep(300), but this does not work. I tested all other code and it works fine until I add a line sleep.

<?php
/**
 * Twitter App
 * bagelBack.php
 * Takes parameters from $_POST and creates a tweet
 * RKoutnik, 2012
 * Code originally found on http://140dev.com/twitter-api-programming-tutorials/hello-twitter-oauth-php/
 */

$name = '@'.$_POST['twitterName'];
$type =  $_POST['bagelType'];

/* BEGIN CONTENT SPINNER TO IMPRESS LYNK */
$bagels = array(
    0 => "bagel",
    1 => "breakfast treat",
    2 => "doughy food-type item",
    3 => "round yeast-raised munchie",
    4 => "doughnut-shaped roll",
    5 => "hard-crusted treat"
);
$finished = array(
    0 => "finished toasting",
    1 => "completed toasting",
    2 => "stopped being raw",
    3 => "concluded the toasting phase",
    4 => "been sucessfully executed",
    5 => "been roasted to a crisp"
);

$food = $bagels[array_rand($bagels)];
$fin = $finished[array_rand($finished)];
sleep(300);
$tweet_text = $name.", Your ".$type." ".$food." has ".$fin;

$result = post_tweet($tweet_text);
echo "Response code: " . $result . "\n";

function post_tweet($tweet_text) {

  // Use Matt Harris' OAuth library to make the connection
  // This lives at: https://github.com/themattharris/tmhOAuth
  require_once('tmhOAuth.php');

  // Set the authorization values
  // In keeping with the OAuth tradition of maximum confusion, 
  // the names of some of these values are different from the Twitter Dev interface
  // user_token is called Access Token on the Dev site
  // user_secret is called Access Token Secret on the Dev site
  // The values here have asterisks to hide the true contents 
  // You need to use the actual values from Twitter
  $connection = new tmhOAuth(array(
    'consumer_key' => '[redacted]',
    'consumer_secret' => '[redacted]',
    'user_token' => '[redacted]',
    'user_secret' => '[redacted]',
    'curl_ssl_verifypeer'   => false
  )); 

  // Make the API call
  $connection->request('POST', 
    $connection->url('1/statuses/update'), 
    array('status' => $tweet_text)
  );

  return $connection->response['code'];
}
?>