From Time Management from the Inside Out:
Another reason people incorrectly estimate how long tasks take is that they overlook hidden time costs. Emily was a novelist whose goal was to write for three hours every morning. So she’d schedule three hours of writing time. That was logical enough; however, she consistently got only two hours of work done each day.
After paying attention to her habits, Emily realized it took her an hour to warm up. During this time, she read the newspaper, drank coffee, and gathered her thoughts. When she skipped this step, her writing was dreadful.
She had to accept that part of her process included warming up. For Emily to write productively for three hours, she needed to schedule four hours. To calculate how long it would take her to write a piece, she would have to allow for this transition time.
It is very interesting that this person spent one hour essentially doing other things in order to get “warmed up” for the writing she intended to do. It would be tempting to say, “that’s inefficient — she should just skip those things, and she’ll get more done in her day.” But, as she noted, if she skipped those “warm-up tasks,” her writing was horrible.
The lesson: Unproductive time is not necessarily unproductive. It may be an essential step in “tuning up” your mind for the high-level tasks it needs to do. If you cut it out, you may find that your productivity decreases rather than increases.
If you find this to be true in your case, embrace it. Don’t go overboard, but don’t try to change yourself. If you can get 4 hours of work done in 4 hours of straight work, that’s great. But if you “waste” the first hour, but then in the remaining 3 hours get the equivalent of 4 hours of tasks done, more power to you.