Like so?

        if data_t.ndim > 2:
            # return list of stcs if transformed data has dimensionality > 2
            if copy:
                stcs = [SourceEstimate(data_t[:, :, a], verts, tmin,
                                       self.tstep, self.subject)
                                       for a in range(data_t.shape[-1])]
            else:
                raise ValueError('copy must be True if transformed data has '
                                 'more than 2 dimensions')
        else:
            # return new or overwritten stc
            stcs = self if not copy else self.copy()
            stcs._data, stcs.vertno = data_t, verts
            stcs.tmin, stcs.times = tmin, times
            print stcs.tmin, stcs.times