Auto delete WordPress users according to time

You can include this code by creating a new custom plugin which help you to stop this when you deactivate the plugin.

wp_schedule_event(time(), 'daily', 'my_dailyClearOut');

function my_clearOldUsers() {
    global $wpdb;

    $query = $wpdb->prepare("SELECT ID FROM $wpdb->users WHERE datediff(now(), user_registered) > 7");

    if ($oldUsers = $wpdb->get_results($query, ARRAY_N)) {
        foreach ($oldUsers as $user_id) {
            wp_delete_user($user_id[0]);
        }
    }
}

add_action('my_dailyClearOut', 'my_clearOldUsers');