Finalizar sessão depois de x minutos

$_SESSION["user_time"];
session_start();

function auto_logout($field){
$t = time();
 $t0 = $_SESSION[$field];
 $diff = $t - $t0;
 if ($diff > 1500 || !isset($t0)){
 return true;
 }
 else{
 $_SESSION[$field] = time();
 }
}

 :seta:

session_start();

function auto_logout($field){

 if( isset( $_SESSION[$field] ) and ( ( time() - $_SESSION[$field] ) > 1500 ) ){
 return true;
 }

 $_SESSION[$field] = time();

 return false;
}

hinom, obrigado. Mas acabei usando outro script:

if (!isset($_SESSION['CREATED'])) {
 $_SESSION['CREATED'] = time();
} else if (time() - $_SESSION['CREATED'] > 300) {
 // session started more than 30 minutes ago
 session_regenerate_id(true); // change session ID for the current session an invalidate old session ID
 $_SESSION['CREATED'] = time(); // update creation time
}

if (isset($_SESSION['LAST_ACTIVITY']) && (time() - $_SESSION['LAST_ACTIVITY'] > 300)) {
 // last request was more than 30 minutes ago
session_unset(); // unset $_SESSION variable for the run-time
 session_destroy(); // destroy session data in storage
}
$_SESSION['LAST_ACTIVITY'] = time(); // update last activity time stamp

blzinha.

esse que vc postou faz a mesma lógica do que eu postei e adiciona tb o tempo de atividade que está faltando no post #1