Peter Drucker writes that if you consolidate at least a quarter of your working time into sufficiently large blocks, it may be enough for the most important parts of your work. And vice versa: 3/4 of your time may be spent in vain if the time blocks are between 15 to 30 minutes.
The important parts of our work, of course, follow from our most important activities or simply coincide with them. Therefore it would be reasonable to find for our main activities the time in the day when the probability of interruption is minimal.
Let us briefly discuss how much time we need to consolidate for an important activity. It of course depends on the activity. For example, if you are just beginning your physical exercise program, say aerobics, and are not in your best physical form, even 5 to 10 minutes could be enough. But if you are in good physical form, to keep it you may need 20-60 minutes 3 to 5 times in a week.
Though there is no general rule and there are many exceptions, usually a serious work (and the workout in particular) requires at least 45 minutes and preferably 2x45 minutes with little break. This is well known in the universities where the duration of the lectures is usually 2x45. But business practice also confirms this. For example, Peter Drucker writes that the manager of a large bank (Drucker's client) told him that he had discovered he could pay attention to a particular task not more than an hour and a half. After this his ability to concentrate diminished, but 1.5 hours was usually just enough to understand the problem and begin to solve it. This client was very busy and the consultations were in his bank but during 1.5 hours they were never interrupted. So it seems that an hour and half a day is usually optimal for a serious task or problem. Then it would be better to switch to another activity or take a long break.
Why it is so important to consolidate time? The point is that our minds are like computers with very large memories. It takes time to upload the operation system into the computer memory from the hard drive when you switch your computer on. But human memory is much larger, and it takes a long time and as you know sometimes takes a lot of effort to upload or at least makes close to our conscious all that we know about the problem. Any interruption may break these association links. The similar is true even for physical work and exercises partly because any work is coordinated by our brain and nerve system and it takes time to "upload the corresponding program". Drucker writes that there are almost no people, who can effectively manage more than two important tasks simultaneously and even this requires much effort if the tasks are complex.
Sometimes there are many small tasks of a similar kind and each task by itself takes a short time. Since they are similar, they require the same mood and "tuning". Therefore, there is reason in "bunching" them together. This consolidation of time for similar tasks is related to the consolidation of activities into one broad category that facilitates keeping these activities in mind as a whole and control of the time spending on them.
For example, let us consider one of our main activities, Relationships. Part of this activity is relationships with colleagues at work, especially with those with whom we meet or work daily. To have good relations with colleagues, it is worthwhile to chat with them regularly about their families, the weather, etc, because otherwise they could decide that they are not interesting to you. These conversations are short but can consume much time if you have many colleagues and friends at work. It would be better to combine all these non-goal oriented but useful talks together and have all of them in a convenient time, say coffee or lunch break. Another example that time manager expert Kathy Prochaska-Cue gives: " ‘bunch’ your out-of-the-office appointments on the same day". I hope you grasp the idea and can modify it to your particular needs.
Though we can choose the time when the interruptions are improbable, they may happen. What we can do to preserve the time consolidation? Many time managers advise two things:
Of course, usually it is impossible and frequently even wrong to be out of reach all day long, but as Drucker says, even 1/4 of working day free from the interruption could be very useful.
"If there is one secret of effectiveness, it is concentration, and effective executives do first things first and they do one thing at a time". (Peter Drucker)
"Given the limited storage capacity of attention and working memory systems, the more an individual must allocate attention to nontemporal information, the less they can allocate to temporal processing..." (Barkley et. al.)
"You will never find time for anything. If you want time, you must make it". (Attributed to: Charles Buxton, 1823-1871, British Author)
"If you haven't got the time to do it right, when will you find the time to do it over?" (Jeffery J. Mayer)
"...in most circumstances, the more time pressure workers experienced, the less creative both they and the authors judged them to be. On the other hand, there was a set of conditions in which creativity did flourish, even under extreme time pressures: ... [when] they could remain focused on the task for significant periods of time without interruption.". (Govendo 2003). (That actually again means no time pressure at least in the consolidated period of time. Vadim Motorine)
"To choose time is to save time" (Francis Bacon)
"Keep in mind that you are always saying "no" to something. If it isn't to the apparent, urgent things in your life, it is probably to the most fundamental, highly important things. Even when the urgent is good, the good can keep you from your best, keep you from your unique contribution, if you let it". (Stephen Covey)
"Between stimulus and response is our greatest power -- the freedom to choose". (Stephen Covey)
"You have to decide what your highest priorities are and have the courage--pleasantly, smilingly, nonapologetically-- to say 'no' to other things. And the way you do that is by having a bigger 'yes' burning inside". (Stephen Covey)