I was a little flummoxed as to how I needed to arrange the values in my Owl Man project to give it a dusk or nighttime feel. One thing that I was taught and has worked for me is to look at how other artists solved a similar problem.
I hunted around to see if I could find a painting where someone solved a similar issue. Thanks to Google, I found artist Larry DeGraff who painted a nocturne using daytime photos and referenced one of Frank Tenney Johnson's western art nocturnes. Both DeGraff's and Johnson's painting helped me get a better idea of where I could push my drawing. I looked at how each artist arranged the values of the various elements and how relatively dark or light those values appear.
Here's a link to Mr. DeGraff's blog post where you see his painting and some of his references. I like how his painting turned out: http://missourivalleyimpressionistsociety.com/blog/56082/painting-a-nocturne-from-daytime-photos