Hi, The documentation mentions the possibility to use a negative offset with a TumblingEventTimeWindows :
// daily tumbling event-time windows offset by -8 hours.input .keyBy(<key selector>) .window(TumblingEventTimeWindows.of(Time.days(1), Time.hours(-8))) .<windowed transformation>(<window function>); But the code will throw an IllegalArgumentException : if (offset < 0 || offset >= size) { throw new IllegalArgumentException("TumblingEventTimeWindows parameters must satisfy 0 <= offset < size"); } Regards, Vladislav