I usually find that morning light is better for hunting. Mid day isn't too bad either. When it gets later in the evening sometimes the shadows make spotting them harder for me. Usually I am hunting flats or north slopes so the morning shadows are not as much of a hinderance.
It really depends on the location. Try to hit your spot when the lighting is as even as it can get. That way the shadows and contrasts don't add to the complexity of your search.
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