

function GetTimeZone: string;
var
  TimeZone: TTimeZoneInformation;
begin
  GetTimeZoneInformation(TimeZone);
  Result := 'GMT ' + IntToStr(TimeZone.Bias div -60);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  label1.Caption := GetTimeZone;
end; 