Why is my cookie not unsetting upon logout?

if (is_user_logged_in()){
    if(!isset($_COOKIE['alertuser'])){
        // set cookie
        $timer = time()+86400;
        setcookie('alertuser', '1' $timer);

        // show alert
        function load_alert(){
            wp_register_script('alert', get_template_directory_uri() . '/js/alert.js', array( 'jquery' ));
            wp_enqueue_script( 'alert');
        }
        add_action('admin_enqueue_scripts', 'load_alert');

    }
} else {
        $timer = time()-86400;
        setcookie('alertuser', '', $timer); // <-problem here
}

I’m trying to attach a js file only when a customer first logs in. Upon signing out the cookie should get deleted, but isn’t. Why?

(Maybe this is more of a php question that WP specific, if so, sorry for posting it here.)