def unpack_dosdate(self, offset):
        """
        Returns a datetime from the DOSDATE and DOSTIME starting at
        the relative offset.
        Arguments:
        - `offset`: The relative offset from the start of the block.
        Throws:
        - `OverrunBufferException`
        """
        try:
            o = self._offset + offset
            return dosdate(self._buf[o:o + 2], self._buf[o + 2:o + 4])
        except struct.error:
            raise OverrunBufferException(o, len(self._buf))