cdm/src/main/java/ucar/nc2/units/SimpleUnit.java
static public boolean isDateUnit(ucar.units.Unit uu) {
    boolean ok = uu.isCompatible(dateReferenceUnit);
    if (!ok) return false;
    try {
      uu.getConverterTo(dateReferenceUnit);
      return true;
    } catch (ConversionException e) {
      return false;
    }
  }
static public boolean isDateUnit(ucar.units.Unit uu) {
    boolean ok = uu.isCompatible(dateReferenceUnit);
    if (!ok) return false;
    try {
      uu.getConverterTo(dateReferenceUnit);
      return true;
    } catch (ConversionException e) {
      return false;
    }
  }
Return true if this ucar.units.Unit is a Date.

@param uu check this Unit
@return true if its a Date