TDateTime - Native date and time value that is the hour offset from UTC.

OffsetFromUTC is a TDateTime function that returns a native date/time value that is the number of hours that the local timezone differs from a date/time expressed in Universal Time Coordinate (UTC). 

OffsetFromUTC is often used to determine the time offset for regions and localities that are subject to Daylight Savings Time conventions. 

OffsetFromUTC can generate an EIdFailedToRetreiveTimeZoneInfo when the timezone cannot be determined. 

On the Linux platform, OffsetFromUTC uses the value in GOffsetFromUTC as the difference from UTC time coordinates.