My most productive fly fishing outings have been after dark. I personally love it. If the fish are feeding, (which it seems they often are) less than perfect drifts and other presentation mistakes seem to be less important. The fish just seem to be hungry, or have lost some of their fear. Besides the water is more likely to be all mine. I am always amazed when fishing and hunting, and I venture into the field before or after daylight how much "night vision" we humans actually possess, once we get away from the light pollution we live with every day. To summarize, I often wait until quite late to venture out.