public long getDisplayWindowBegin() {
    return displayWindowBegin;
  }
Display window begin will be set to the same as the minimum timestamp of the query result set,
and display window end will be set to the same as the maximum timestamp of the query result
set. delta default equals 0.
iotdb-api/udf-api/src/main/java/org/apache/iotdb/udf/api/customizer/strategy/StateWindowAccessStrategy.java