Опция использует функцию Datetime :
FORMAT_DATETIME(format_string, datetime_expression)
Например:
bq query --nouse_legacy_sql \
"SELECT FORMAT_DATETIME('%Y-%m-%d %H:%M:%S', '2020-01-01 13:45:55') AS datetime;"
+---------------------+
| datetime |
+---------------------+
| 2020-01-01 13:45:55 |
+---------------------+