It is currently possible to specify an "offset" for tumbling / sliding windows. The offset is however immutable. This creates a problem for aggregations that have to be performed in a timezone which utilises daylight savings time for half of the year. For example. If one is aggregating data by day in the New York time zone, then for half of the year, the offset is 5 hours (relative UTC) and for the other half of the year, the offset is 4 hours (relative UTC). There is no way to construct tumbling / sliding windows to specify daylight savings time behaviour. It would be helpful if there was a constructor for tumbling / sliding windows to specify the timezone that the aggregation must be performed in (default = UTC). The tumbling / sliding window would then be required to automatically change the offset depending on whether daylight savings time is active or not for the specified time zone. My application is using the DataStream API.