- char start_datetime[sizeof("YYYYmmddTHHMMSS+HHMM")] = {};
- char end_datetime_suffix[sizeof("-YYYYmmddTHHMMSS+HHMM")] = {};
+ char start_datetime[ISO8601_STR_LEN] = {};
+ /* Add 1 for a '-' prefix. */
+ char end_datetime_suffix[ISO8601_STR_LEN + 1] = {};