PHP sleep() ne fonctionne pas

Je suis en train de faire un fichier php qui va lancer un événement après un délai de cinq minutes. De la documentation, il semble que d'attendre cinq minutes n'aurait besoin que d' sleep(300), mais ce n'est pas de travail. J'ai testé tous les autres codes, et il fonctionne très bien jusqu'à ce que je ajouter de la sleep ligne.

<?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'];
}
?>