Fixed logic...

First argument, specifying the frequency, can be an integer *or* a character.

src/@dates/dates.m

@@ -112,7 +112,7 @@ methods
             end
             return
         end
-        if isequal(nargin,4) && isfreq(varargin{1}) && isequal(varargin{1},365)
+        if isequal(nargin,4) && isfreq(varargin{1}) && ( isequal(varargin{1},365) || strcmpi(varargin{1},'D'))
             o.time = NaN(0,2);
             if ischar(varargin{1})
                 o.freq = string2freq(varargin{1});