[sergioisidoro]

Ah! you are correct. I thought the author was referring to the possibility of a country south of another being 1h ahead/behind depending if they do the yearly switch or not.

But in this case we go to the general problem of choosing of timezones. You have plenty of cases of south borders with different timezones (ie. without moving in longitude you still switch zones).

It's a matter of country size, not to mention that it is a matter of economic interest to keep the same timezone as neighbouring countries. I would assume the scenario you mentioned to be quite unlikely.