code: def get_time_graded(self):
          
          if not self.is_graded() or self.is_derived():
              raise errors.IllegalState()
          time_graded = self._my_map['timeGraded']
          return DateTime(
              year=time_graded.year,
              month=time_graded.month,
              day=time_graded.day,
              hour=time_graded.hour,
              minute=time_graded.minute,
              second=time_graded.second,
              microsecond=time_graded.microsecond)
docs: Gets the time the gradeable object was graded.
  
          return: (osid.calendaring.DateTime) - the timestamp of the
                  grading entry
          raise:  IllegalState - ``is_graded()`` is ``false`` or
                  ``is_derived()`` is ``true``
          *compliance: mandatory -- This method must be implemented.*