If we plan something and cannot accomplish it in-time because we misjudged it or some odds happen, we can never plan an buffer and expect it to cusion us and set us free from worries of over-running our schedule times. Here is my approach and reply to what Scotty said on the99percent.com's blog.
Where I agree with Scotty's approach of keeping a margin between two schedules, I want to share this would prove unproductive when things finish on time and even when they don't, the margin might appear insufficient still leaving chances for a ripple effect in the tasks planned after the margin time. We can never plan accurately, when we cannot plan our planned activities with certainty, we can surely not plan our margins or utilize them expecting them to solve everything.
The next generation approach to solve the same problem would be to realize that there are few things which are important and some are probably not and also the fact that some planned activities will surely get compromised. When we are able to make a distinction between important and compromise-able tasks, then we will still utilize the whole day, without giving any margins or empty slots, and still able to get most value out of time. That means we would need to have one important and couple of unimportant tasks in-between and then another important task planned in a line. In that way, if we have to comprise some task inevitably, we would only compromise a minor one instead of hurting something which is equally important.
Now there is another level of approach which supersedes this important and compromise-able schedules approach and that is sense of direction. If we know we are moving in the right direction, doing right tasks and giving right time to the work, the sense of losing appointments wouldn't hurt. Disturbance in schedule is ought to happen but whenever it does, it wouldn't disturb our sense of professional accomplishment.
Now for a moment, forgetting all the “next-gen” approaches, if we stick to our daily tightly planned schedules, if we give extra time to some task it would be better to take planned one task out and reschedule for the coming day instead of disturbing all the tasks lying next in line and completing them just for the sake of it. That means you must not plan whole week ahead but only a day or two at most. That means the buffer which you are trying to create within the same day should exist in the form of next day or the days after that and that would save time and solve this unplanned and time-stretches issues.