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

No. The gap stays at 1h all year.

When is the best time to call Jakarta from Hong Kong?

Between 10:00 and 17:00 in Hong Kong, which is 09:00 to 16:00 in Jakarta.

Hong Kong is 1h ahead of Jakarta. This gap is the same all year — neither city shifts its clocks relative to the other.

Hong Kong

Hong Kong SAR China

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Jakarta

Indonesia

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A 9-to-5 day in each city overlaps for 7h. That is 10:00–17:00 in Hong Kong, which is 09:00–16:00 in Jakarta.

City	Time zone	UTC offset
Hong Kong · Hong Kong SAR China	Asia/Hong_Kong	UTC+8
Jakarta · Indonesia	Asia/Jakarta	UTC+7

What is the time difference between Hong Kong and Jakarta?: Hong Kong is 1h ahead of Jakarta. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Hong Kong and Jakarta change during the year?: No. The gap stays at 1h all year.
When is the best time to call Jakarta from Hong Kong?: Between 10:00 and 17:00 in Hong Kong, which is 09:00 to 16:00 in Jakarta.