public void Foo() { DateTimeZone zone = DateTimeZoneProviders.Tzdb["Europe/Astrakhan"]; DateTimeZone localZone = DateTimeZoneProviders.Tzdb["Europe/Berlin"]; var activity = ActivityHelper.CreateForTime("Foo", 2019, 5, 1, 10, 0, 60, zone); activity.Begin.Hour.Should().Be(10); activity.Begin.Day.Should().Be(1); var localBegin = activity.Begin.WithZone(localZone); localBegin.Hour.Should().Be(8); }