Does the time difference between Jakarta and Rome change during the year?

Yes. Because of daylight saving time the gap moves between +5h and +6h.

When is the best time to call Rome from Jakarta?

Between 14:00 and 17:00 in Jakarta, which is 09:00 to 12:00 in Rome.

Jakarta is 5h ahead of Rome. This gap is not fixed: daylight saving time moves it between +5h and +6h during the year.

Jakarta

Indonesia

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Rome

Italy

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A 9-to-5 day in each city overlaps for 3h. That is 14:00–17:00 in Jakarta, which is 09:00–12:00 in Rome.

City	Time zone	UTC offset
Jakarta · Indonesia	Asia/Jakarta	UTC+7
Rome · Italy	Europe/Rome	UTC+2

What is the time difference between Jakarta and Rome?: Jakarta is 5h ahead of Rome. This gap is not fixed: daylight saving time moves it between +5h and +6h during the year.
Does the time difference between Jakarta and Rome change during the year?: Yes. Because of daylight saving time the gap moves between +5h and +6h.
When is the best time to call Rome from Jakarta?: Between 14:00 and 17:00 in Jakarta, which is 09:00 to 12:00 in Rome.