public function getURL($start_timestamp = 0, $calendar_guid = 0) {
		if (!$start_timestamp) {
			$start_timestamp = $this->getNextOccurrence();
		}
		$url = parent::getURL();
		return elgg_http_add_url_query_elements($url, array_filter(array(
			'ts' => $start_timestamp,
			'calendar' => $calendar_guid,
		)));
	}