procedure TForm1.FormCreate(Sender: TObject);
begin
  Memo1.Clear;
  with TRegistry.Create(KEY_WOW64_64KEY or KEY_ALL_ACCESS) do
  try
    RootKey := HKEY_LOCAL_MACHINE;
    if OpenKey('SOFTWARE\Microsoft\Windows NT\CurrentVersion', False) then
    begin
      Memo1.Lines.Add(IntToStr(ReadInteger('InstallDate')));//1398998255
      Memo1.Lines.Add(DateTimeToStr(UnixToDateTime(ReadInteger('InstallDate'))));//2014-05-02 2:37:35
      Memo1.Lines.Add(DateTimeToStr(UnixToDateTime(ReadInteger('InstallDate') + 28800))); //2014-05-02 10:37:35
      Memo1.Lines.Add(DateTimeToStr(JavaToDelphiDateTime(ReadInteger('InstallDate'))));// 1970-01-17 12:36:38
    end;
  finally
    Free
  end;
end;

Unix时间戳转换成Delphi的TDateTime
function UnixDateToDateTime(const USec: Longint): TDateTime;
const
  cUnixStartDate: TDateTime = 25569.0; // 1970/01/01
begin
  Result := (Usec / 86400) + cUnixStartDate;
end;

{ Unix date conversion support } RTL

HoursPerDay = 24;
MinsPerHour = 60;
SecsPerMin = 60;
MSecsPerSec = 1000;
MinsPerDay = HoursPerDay * MinsPerHour;
SecsPerDay = MinsPerDay * SecsPerMin;
MSecsPerDay = SecsPerDay * MSecsPerSec;

{ Days between 1/1/0001 and 12/31/1899 }

DateDelta = 693594;

{ Days between TDateTime basis (12/31/1899) and Unix time_t basis (1/1/1970) }

UnixDateDelta = 25569;

function DateTimeToUnix(const AValue: TDateTime): Int64;
begin
  Result := Round((AValue - UnixDateDelta) * SecsPerDay);
end;

function UnixToDateTime(const AValue: Int64): TDateTime;
begin
  Result := AValue / SecsPerDay + UnixDateDelta;
end;