The best time for shots like these, is a day with high overcast clouds. That way, the whole owl is in the shade. Sunny days are good for being able to see, but for photography, I prefer light clouds.
Even for birds not in the woods, sunny conditions make for overly contrasty light. Mornings and late afternoons usually have the best light, hence the golden hour.
The nice thing about winter, is that the sun is lower in the horizon all day, and snow on the grounds works very well as a reflector to fill in the shadows.