grib/src/main/java/ucar/nc2/grib/coord/CoordinateTimeIntv.java
@Override
  public CalendarDateRange makeCalendarDateRange(ucar.nc2.time.Calendar cal) {
    CalendarDateUnit cdu = CalendarDateUnit.of(cal, timeUnit.getField(), refDate);
    CalendarDate start = cdu.makeCalendarDate( timeUnit.getValue() * timeIntervals.get(0).getBounds2());
    CalendarDate end = cdu.makeCalendarDate(timeUnit.getValue() * timeIntervals.get(getSize()-1).getBounds2());
    return CalendarDateRange.of(start, end);
  }
@Override
  public CalendarDateRange makeCalendarDateRange(ucar.nc2.time.Calendar cal) {
    CalendarDateUnit cdu = CalendarDateUnit.of(cal, timeUnit.getField(), refDate);
    CalendarDate start = cdu.makeCalendarDate( timeUnit.getValue() * timeIntervals.get(0).getBounds2());
    CalendarDate end = cdu.makeCalendarDate(timeUnit.getValue() * timeIntervals.get(getSize()-1).getBounds2());
    return CalendarDateRange.of(start, end);
  }
Make calendar date range, using the first and last ending bounds
@param cal  optional calendar, may be null
@return  calendar date range