Once upon a time, before I had kids, before I had more kids, before I taught creative writing at UBC, before I left UBC to edit and mentor privately, I had the luxury of fourteen hour stretches of writing. I would write all day and into the night. And, well, burn myself out. All that time spent at the keyboard ended up being counterproductive. I ended up spending much of that writing time doing other things, to avoid the work.
Now my writing time is precious, something I grab when I can, between interruptions. And I've learned that I really only have three or four hours of writing in me in any given work day. Writing requires deep focus and is difficult mental work. If I push past that four hour mark, I'm fried the next day and get nothing done. So I've learned to pace myself.
I was a night owl once, but now, as I grown older, I get my writing done in the morning hours, while my mind is fresh (and when there are fewer interruptions in my day). The rest of my writing day is spent on research and preparing for the next day of writing. This preparation, of course, makes all the difference. My mind knows which direction I'm heading and churns away overnight on the problem. The solutions are so often there for me the next morning.
And, of course, the reality is that writing is a business, like any other. I have no end of administrative details to take care of. So that takes up a good chunk of the day.
Then there's that one last important element to this writer's day: procrastination. My mind needs time to hash out a problem, so, recognizing that, I build mindless tasks into the day. My most productive "writing time" occurs when I'm away from the keyboard: doing the dishes, the laundry, or, most often, taking a walk down. It's here that inspiration strikes.
So, my advice to apprentice writers on the subject of time management: don't kick yourself if you can't get more than an hour or two of writing in a day. Most of us lead very busy lives. If you write 250 words a day, and you can certainly do that in an hour or two, you'll have a rough draft of a novel done in a year. Novelists are plodders: one little step at a time ...