Решил проблему. Код не «оптимизирован», но работает:
CallTimeDouble := StrToInt64(DATEx) / 1000; //Gives seconds
CallTimeDouble := CallTimeDouble / 60; //Gives Minutes
CallTimeDouble := CallTimeDouble / 60; //Gives hours
CallTimeDOuble := CallTimeDouble / 24; //Gives dates
CallTimeDouble := CallTimeDouble + 25569; //01.01.1970 - 30.12.1899
CallTimeDouble := CallTimeDouble + 0.125; //Added +3h to GMT, Finland
Result := CACHED_NAMEx + ' ' + NUMBERx + ' ' + FormatDateTime('dd.mm.yyyy hh:mm:ss', CallTimeDouble) + ' ' + DURATIONx;
ShowMessage(Result);