public function col_duration($row) : string {
        $duration = round($row->timeend - $row->timestart, 2);

        if (empty($duration)) {
            // The format_time function returns 'now' when the difference is exactly 0.
            // Note: format_time performs concatenation in exactly this fashion so we should do this for consistency.
            return '0 ' . get_string('secs', 'moodle');
        }

        return format_time($duration);
    }