Are you a night owl or a morning person? If you are a night person, you may want to try coming up with new fiction ideas and solving old ones in the morning. If you are a day person, the best time is in the afternoon. This data comes from Mareike Wieth and Rose Zacks as found in the article "To Speed Up The Creative Process, Slow Down" by Sam McNerney. According to the research, it turns out you are better at creative thinking at non-peak times.
I found this information through a long and tangled path whose trail head began with Sue Shellenbarger's article "The Peak Time for Everything" and ended with Sam McNerny's. But it was intriguing enough to make me wonder how true this is and which person I am. I feel that I am a natural night owl, but because of my career, I have been forced into a day-time rhythm. As for as creative ideas go, I generally record date and time for many writing-related things, but not always. I'll report back in if I have enough data to figure out how true any of this is for me.
Cite: McNerney, Sam. "To Speed Up the Creative Process, Slow Down." Why We Reason. N.p., 10 Feb. 2012. Web. 27 Sept. 2012.