grib/src/main/java/ucar/nc2/grib/grib2/table/NwsMetDevTables.java
@Override
  public double getForecastTimeIntervalSizeInHours(Grib2Pds pds) {
    Grib2Pds.PdsInterval pdsIntv = (Grib2Pds.PdsInterval) pds;

    // override here only if timeRangeUnit = 255
    boolean needOverride = false;
    for (Grib2Pds.TimeInterval ti : pdsIntv.getTimeIntervals()) {
      needOverride = (ti.timeRangeUnit == 255);
    }
    if (!needOverride)
      return super.getForecastTimeIntervalSizeInHours(pds);


    return 12.0;
  }
@Override
  public double getForecastTimeIntervalSizeInHours(Grib2Pds pds) {
    Grib2Pds.PdsInterval pdsIntv = (Grib2Pds.PdsInterval) pds;

    // override here only if timeRangeUnit = 255
    boolean needOverride = false;
    for (Grib2Pds.TimeInterval ti : pdsIntv.getTimeIntervals()) {
      needOverride = (ti.timeRangeUnit == 255);
    }
    if (!needOverride)
      return super.getForecastTimeIntervalSizeInHours(pds);


    return 12.0;
  }
Only use in GribVariable to decide on variable identity when intvMerge = false.
By returning a constant, we dont intvMerge = false.
Problem is we cant reconstruct interval length without reference time, which is not in the pds.