To answer your question - Yes.

In point of fact, the observation of no interruption for the team (by anyone including management) means more work is done in less hours. This observation, which I have found to be true, was made in the late 80's.

Any interruption in thought processes when doing engineering/technical work requires the person to spend a significant amount of time returning to the place where the interruption occurred.

Management practise since the late 80's has ensured that all technical staff (engineering, programmers, etc) must be interruptible at all times (especially by management itself). The team/team members have no ability to redirect phone calls, email messages or management meetings to management PA's to deal with.

The experience that I and my technical colleagues had was that if we could have a non-interrupted period of 2-3 hours to work on any project, we would achieve more than we could in any normal interrupted 8 hour day. Often we found that an extended uninterrupted period of 4-6 hours would allow us to complete technical work/projects that would normally take us a week to complete. This was based on a total effective 1 hour due to the continual interruptions we normally received during our normal days. This lead us to start work early and finish late when we could work uninterrupted. Of course, this worked against as this was in effect unpaid time.

The common management practise of the last 30 years has ensured that every technical/engineering team works at its lowest efficiency. There are some managers who will protect their engineering teams from such interference and as a consequence get a much higher efficiency out them in a normal work day of 7-8 hours. Unfortunately, these kinds of managers are few and far between.

I would say that any team that works beyond this number of hours will still not achieve anywhere near the same results as a corresponding team that has the unfettered ability to block out all interruptions.

In addition, it also requires group offices for this to work. Open plan layouts are an instant cause of inefficiency, especially with technical/engineering groups. Two to three team members per office would be ideal.

As an office is considered a status symbol within management circles, we should not expect any sensible outcome in this area. All of this was documented and published in the late 80's.

In relation to your comment that in any day there is only 4 hours that you write solid code, I would suggest that if you had an uninterrupted 4 hours that the amount of code produced would very likely double or even triple and be even better.

Just don't expect any management or management guru's of today to see it this way.

The comment regarding brain-intensive work being fatiguing is certainly true when you have to deal with multiple interruptions. From my experience, mostly the fatigue is from having to get yourself back to the place you were at before the interruption. A uninterrupted period of time devoted to a brain-intensive activity is less stressful than the same period that has had interruptions.

I am also saying that such periods of time need to be regulated by oneself so that burnout doesn't occur. Good physical activity, good food, rest, relaxation and good non-work related socialising make one able to keep at peak efficiency.

Have made some edits about to fill in more explanation and correct spelling and sentence structure.