I read a fascinating post by novelist Lydia Sharp in which she described having what she calls Seasonal Writing Disorder. It's well worth reading the entire post, but in a nutshell she said she used to beat herself up because not only does she not write every day, she goes weeks without writing.
Then she realized that if she stepped back and looked at her ouput in the context of a year, she was just as productive as other writers, if not more so. Like me, she suffers from Seasonal Affective Disorder, which is characterized by depression and low energy during the darker months. I use a bright light in the mornings during the winter, which helps a bit.
Sharp is most productive in Spring--that's when she has written six of her seven novels. Spring and early Summer are also my favorite times and probably my most productive times.
Your cycles may be different. The point is that when you discover what they are you can work in synch with them rather than fighting them or feeling bad about not working in some supposedly ideal manner.
This doesn't mean that you can move forward only a few months of the year. The times during which you don't feel as inspired can be great for editing, marketing, and learning new skills.
Of course the same is true of getting in tune with your daily cycle, doing the most important tasks during the time you have the most energy. Especially if morning is your prime time, it's a shame to spend it on catching up with email, for instance.
It's in line with a sayig I like: "Make reality your friend."
(There are time management tips you can use all the year around in my book, Focus: use the power of targeted thinking to get more done. It's published by Pearson and avialable from Amazon or your other favorite bookseller.)