como saber cuando caduca una cookie

[PHPeros]

Código PHP:

$expiry = time() + 12345;
$data = (object) array( "value1" => "just for fun", "value2" => "i'll save whatever I want here" );
$cookieData = (object) array( "data" => $data, "expiry" => $expiry );
setcookie( "cookiename", json_encode( $cookieData ), $expiry );
 
$cookie = json_decode( $_COOKIE[ "cookiename" ] );
 
$expiry = $cookie->expiry;
 

Copiado y pegado de StackOverflow.