Much of writing is intangible. The arranging and changing of words on a page to represent a story would be a strange concept to anyone who hadn't been raised on stories. But at least you can see the words. The thinking time put into any piece of writing even more intangible. Inspiration tends to strike when I'm in the middle of something completely unrelated to writing - often in the shower, when writing it down is rather difficult!
Resting... or Slacking?
I think it helps to take a break from consciously trying to solve writing problems. Once I stop going over how on Earth I'm going to get this character from A to B, the solution comes to me. A great piece of dialogue pops into my head when I'm putting on makeup. An idea for a story comes to me when I'm cooking dinner.
The rest period is important. Ask any sportsperson. However, I'm also aware of how 'resting' can be used as an excuse to avoid work!
Writing is difficult to quantify: if I write 2000 words today and 1000 words tomorrow, it doesn't mean I've worked twice as hard today. Nor does it mean today's work is better simply because there appears to be more. The time spent thinking about writing often has an impact on the quality of the work, as does the quality of the thinking itself - this is where I slip up.
When I'm typing, I usually have my internet browser open and play games as I think/write. I usually choose simple puzzle games, so I don't need to be absorbed in the game and fall into a rhythm that helps me think. However, I confess that sometimes I'm not doing much thinking - I'm just playing games...
Finding a Balance
It's hard to catch yourself when thinking about writing lapses into thinking about getting a high score, or whatever else you should be doing. Sometimes I do the opposite: I berate myself for wasting time when I've actually managed to think through several problems. Trouble is, it's not always reflected in the page. That's my problem: working out whether the thinking is productive.
The only solution I can think of is to assess my writing habits over a long(ish) period: if I haven't produced any writing over the course of two weeks, for example, something's wrong and I need to change. If, on the other hand, I manage to finish stories and keep up with my MA assignments/exercises despite feeling I've wasted hours, I should probably cut myself some slack. It's either that or find work as a professional time-waster!