switch($_POST['t']) {
    case 'updates': {
                            if(isset($_POST['ts']) || !empty($_POST['ts'])) {
                                    $query = $pdo->prepare('UPDATE users SET user_activity_ts = :activity WHERE id = '. intval(1) .''); // 1 it's temp value :P

                                    $query->bindValue(':activity', time());

                                    $query->execute();


                                    $query2 = $pdo->prepare('SELECT user_activity_ts FROM users WHERE user_activity_ts < time() - 5')
                           }





    }
    break;
}