Server Time Zone and Server GMT Offset are the actual offsets for the server time. Note that the offset for a given time zone may be different during different times of year, hence the difference between GTB Standard Time with a GMT offset of 2 and GTB Daylight Time with a GMT Offset of 3. Apparently at this time of year it is GTB Daylight.
Similar, where I live its Eastern Daylight Time now so we are -4 GMT, but next month I think we fall back an hour to Eastern Standard Time which is -5 GMT.
Preferred GMT Offset can be set in user.config with
<add key="PreferredGreenwichMeantimeOffset" value="-5.00" />
so if your server local time is the same as your preferred time zone then set it to 3 for now and change it to 2 when Daylight savings time is over.
Like I said in a different thread, now 3.5 .NET has a TimeZoneInfo class that we will use in the future to make it so we don't have to adjust it manually because this class knows how to adjust it automatically.