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Demystifying project task duration

Patrick Weaver
May 16, 2012

Probably the most common action undertaken by project planners everywhere is assigning a duration to a task; most of us do this almost automatically. Generally it is only when a dispute arises that the complex interaction of the factors discussed involved in setting the duration come into play.

There is no universal answer to the question of what is the ‘correct’ way to assess durations but here is an overview of the multiple factors that should be considered by competent planners and managers.

The initial planning decisions concern the project framework used to define the task:

  • Sizing the time units: Just because your software can calculate in minutes this is not always appropriate: time units of days, weeks and in some cases even months may provide a clearer picture of the overall flow of work in a project.
  • Setting appropriate work periods: 24 x 7, 5 x 8, etc.
  • Determining the task: Choosing an appropriate task is critical; key factors include being the responsibility of a single management entity, capable of being worked on continuously and unambiguous in its scope.

Once the task is determined, and the overall project framework set; the issues concerning the estimation of the optimum task duration come into play.

Some of the factors that may influence the final answer include:

  • The expectations of the person doing the work.
  • Prior expectations: previous experience sets management’s expectations.
  • Volume of work and production rates (but these are highly variable).
  • Optimum crew sizes and the production ‘J’ curve.
  • Capacity and capability of resources.
  • Work methods and physical constraints—efficiency of working.
  • Understanding variability (PERT, Monte Carlo).
  • Setting new expectations: the ‘Critical Chain’ effect of using stretch targets as motivators.
  • Achieving quality (adequate time for testing, etc).

Once the optimum duration of each task has been determined, the next factor to consider is the overall scheduling process, balancing schedule logic, working times, task durations and resources to achieve the overall project objectives, while allowing appropriate contingency times for risks.

This process frequently requires adjustments to the pre-determined optimum duration for a task to achieve contractual objectives, balance resources and/or meet imposed constraints. But this is only the beginning…

As the project progresses, the need to accelerate frequently arises, generally caused by a delaying factor earlier in the project. Reducing the overall duration of the remaining part of the schedule is relatively simple on paper, however achieving acceleration in the workplace is altogether more difficult.

Some of the factors to be considered are:

  • The degree of change required to production levels.
  • The increased risks, resource and management issues associated with fast tracking.
  • The inefficiencies, increased resource and management issues associated with ‘crashing’ durations.

When confronted with the need to accelerate, it is probably wise to think vary carefully about what fundamental changes will be made before simply cutting a few durations. And the critical thing about fundamental change is that it is usually expensive! The best way to avoid problems seems to be starting a project ‘right’.

This focus of this post has been a brief overview of the complexity that lies behind every decision to allocate or change a task’s duration. The process is nowhere near as simple as just picking a number that looks right!

Patrick Weaver
Patrick Weaver is the managing director of Mosaic Project Services and the business manager of Stakeholder Management Pty Ltd. He has been a member of both PMI and AIPM since 1986 and is a member of the Asia Pacific Forum of the Chartered Institute of Building. In addition to his work on ISO 21500, he has contributed to a range of standards developments with PMI, CIOB and AIPM.
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