窗口开始时间反映在 ROWTIME 以及Kafka消息的时间戳。您可以使用用于处理kafka消息的标准api访问此时间戳。
阿飞 kafka-console-consumer 不支持显示时间戳。不管怎样 kafkacat 做。
下面是ksql中的一些聚合数据 ROWTIME 显示窗口的开始（和 TIMESTAMPTOSTRING 习惯了漂亮的印刷品）：

ksql> SELECT TIMESTAMPTOSTRING(ROWTIME, 'yyyy-MM-dd HH:mm:ss'), ROWTIME, STARS, STAR_COUNT FROM RATINGS_AGG2;
2018-06-27 09:30:00 | 1530091800000 | 1 | 2
2018-06-27 09:30:00 | 1530091800000 | 4 | 6
2018-06-27 09:30:00 | 1530091800000 | 2 | 2
2018-06-27 09:30:00 | 1530091800000 | 3 | 3

同样的主题 kafkacat :

$ kafkacat -b localhost:9092 -C -K: \
  -f '\nTimestamp: %T\t\tValue (%S bytes): %s' \
  -t RATINGS_AGG2

Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":1,"STARS":1}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":2,"STARS":1}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":3,"STARS":3}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":5,"STARS":1}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":6,"STARS":3}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":7,"STARS":1}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":7,"STARS":3}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":9,"STARS":1}
Timestamp: 1530091800000                Value (26 bytes): {"STAR_COUNT":9,"STARS":3}

你试过Kafka控制台消费者选项吗 print.timestamp=true ?

$ kafka-console-consumer --property print.timestamp=true ...