The biggest factor in your output as a writer isn't the amount of time you spend writing. It's how effectively you use your time.
Thus if you want to be a productive writer, you should have an accurate sense of how you spend that time.
That's where a daily time log comes in. By logging your time over a sample period of a few days or a week, you can find out precisely how you allocate the hours of your day.
You'll to be shocked by what you find. Most of us hold delusionally inaccurate perceptions of how we spend our days, and it's both sobering and exciting to see how much surplus time really have, especially when we deliberately reallocate it to more useful pursuits.
You'll also discover a wonderful side-benefit: the very act of logging your time causes you to be far less wasteful with it.
The process should be as simple as possible: Use a simple paper notebook or a text file on your computer, and record your activities in half hour chunks all day.
Do this exercise as accurately, honestly and dispassionately as you can. Record the time you spend on time-wasting activities as carefully as you record the time you spend on more important things. The point of this exercise is not to judge yourself--the point is to gather data to help you make the best possible use of your time.
Remember, what gets measured gets controlled. Measure your time and you'll control your destiny as a writer.