the conversion from 1970,1,1 needs the double rounded to zero decimal places i thinks
DateTime d1 = new DateTime(1970, 1, 1);
DateTime d2 = dt.ToUniversalTime();
TimeSpan ts = new TimeSpan(d2.Ticks - d1.Ticks);
return Math.Round( ts.TotalMilliseconds,0);
on the client side i use
new Date(+data.replace(/\D/g, ''));