Does the time difference between Hong Kong and São Paulo change during the year?

No. The gap stays at 11h all year.

When is the best time to call São Paulo from Hong Kong?

There is no overlap between standard working days, so one side has to call early or late.

Hong Kong is 11h ahead of São Paulo. This gap is the same all year — neither city shifts its clocks relative to the other.

Hong Kong

Hong Kong SAR China

--:--:--

São Paulo

Brazil

--:--:--

A 9-to-5 working day in Hong Kong does not overlap one in São Paulo at all — somebody has to take the call outside office hours.

City	Time zone	UTC offset
Hong Kong · Hong Kong SAR China	Asia/Hong_Kong	UTC+8
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between Hong Kong and São Paulo?: Hong Kong is 11h ahead of São Paulo. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Hong Kong and São Paulo change during the year?: No. The gap stays at 11h all year.
When is the best time to call São Paulo from Hong Kong?: There is no overlap between standard working days, so one side has to call early or late.