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

No. Both cities keep the same local time all year.

When is the best time to call Rome from Paris?

Between 09:00 and 17:00 in Paris, which is 09:00 to 17:00 in Rome.

Paris and Rome are on the same local time. This gap is the same all year — neither city shifts its clocks relative to the other.

Paris

France

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Rome

Italy

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A 9-to-5 day in each city overlaps for 8h. That is 09:00–17:00 in Paris, which is 09:00–17:00 in Rome.

City	Time zone	UTC offset
Paris · France	Europe/Paris	UTC+2
Rome · Italy	Europe/Rome	UTC+2

What is the time difference between Paris and Rome?: Paris and Rome are on the same local time. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Paris and Rome change during the year?: No. Both cities keep the same local time all year.
When is the best time to call Rome from Paris?: Between 09:00 and 17:00 in Paris, which is 09:00 to 17:00 in Rome.