I have friends, however, who cringe at the thought of writing early in the morning. Their creative juices start flowing much, much later in the day than mine do.
Does that mean I never write at night? Of course not. There have been times when I've either been so caught up in a book that I didn't want to stop even though I could feel myself tiring and becoming less focused. At other times, I simply had to write into the wee hours because the work had to get done.
That said, I really do think that the work comes alive, it dances, it zings much more when we each pay attention to our inner clock. And that middle of the night writing I've done? Well, I can guarantee that when it came time to edit that work, I was editing during prime time for me. Daytime.
As an example of another way time of day can affect the work, I, like almost every author, keep paper by my bed (because I can guarantee that if an idea comes to me in the middle of the night, it won't be there when I wake up the next day if I don't scribble it down). That said, I've arisen the next morning on numerous occasions to stare at my hastily scribbled, middle-of-the-night notes to think that aliens must have entered my room and written on my pad of paper during the night. The idea in question was so bizarre or worse, lame, that it couldn't possibly have come from me. Needless to say, I rarely harvest good ideas this way (though I keep trying), but I'm betting that the late nighters frequently come up with gems on their nightstand pads of paper.
Oh well, we're all different. We each have our strengths and our best time to create. All we have to do is...learn what time of day we're most creative and then seize the best hours of the day. Don't let anything interfere (or interfere too often) if you can help it. I guarantee that your writing will be better for it.