public void SpecifyTimeZoneDaylightTest() { var dt = new DateTime(1990, 2, 1, 12, 0, 0, DateTimeKind.Local); // just a test var tz = TimeZoneService.FindSystemTimeZoneById("Central Standard Time"); var result = TimeZoneService.SpecifyTimeZone(dt, tz); result.Hour.Should() .Be(12); // same result.Offset.Should() .Be(TimeSpan.FromHours(-6)); }