Autoresponders Interval

function autoresponder_scheduling() {
        wp_clear_scheduled_hook($this -> pre . '_autoresponders');

        $schedules = wp_get_schedules();
        $interval = $this -> get_option('autoresponderscheduling');
        $new_timestamp = time() + $schedules[$interval]['interval'];
        wp_schedule_event($new_timestamp, $interval, $this -> pre . '_autoresponders');

        return true;
    }