program DateRegistry;

uses
  Windows,
  Dialogs,
  Registry,
  SysUtils;


{$R *.RES}

procedure SaveDate(const sKey: string; const sField: string; aDate: TDateTime);
begin
  with TRegistry.Create do
  begin
    RootKey := HKEY_CURRENT_USER;
    if OpenKey(sKey, True) then
    begin
      WriteBinaryData(sField, aDate, SizeOf(aDate));
      CloseKey;
    end;
    Free;
  end;
end;

function ReadDate(const sKey: string; const sField: string) : TDateTime;
begin
  // default: return 0
  Result := 0;

  with TRegistry.Create do
  begin
    RootKey := HKEY_CURRENT_USER;
    if OpenKey(sKey, False) then
    begin
      try
        ReadBinaryData(sField, Result, SizeOf(Result));
      except

      end;
      CloseKey;
    end;
    Free;
  end;
end;

var
  dDate: TDateTime;

begin
  // save the date
  SaveDate('\Software\preview\Demo', 'LastDate', Now);

  // retrieve it
  dDate := ReadDate('\Software\preview\Demo', 'LastDate');

  // show it
  ShowMessage(DateTimeToStr(dDate));
end.