Scheduling Blog Series Part 4: Devil’s in the Duration

Schedule Blog Series Part 4: Devil’s in the Duration


A project schedule is constructed with activities.  Activities represent individual pieces of work, which when organized properly, define how the project is to get completed.  Activities embody a name, duration, and optionally other data.  This article will discuss determining duration.

Type of Project Influences Duration Determination

How well you know the means and methods of executing your activities determines how you should estimate durations.  Some projects have as their product a plan for an execution project. This requires managerial judgement to balance the quality and availability of resources to the goals of the plan.  This process is called Top-Down Estimating.  Judgement with simple math is sufficient for estimating durations.  If sponsors expect the project to be completed within a time frame, allow an activity with 10-30% of the total duration for what’s known as “management reserve.”   A good Top-Down reference for many spheres of endeavor is the Pre-Project Planning manual by the Construction Industry Institute. 

An execution project produces something unique and tangible: a book, building, production facility, software, calculations, a rocket, control system, procedure, corporate charter, a drug.  Many of these projects use means and methods whose labor quantity is available from estimating libraries.  Labor quantity is given in man-hours.  This, and the number of resources you plan to assign to the activity, and how efficiently the resources can work, determines duration.

Where the “Devil” Lay

Credit for the phrase, “The Devil’s in the Details,” goes to Adm. Hyman Rickover, the creator of the nuclear Navy.

Excessive Top-Down judgement in the execution schedule

Projects can have hundreds of activities.  The “Devil” arises when activities whos durations are derived solely from judgement are linked in series.  Errors in the durations multiply.  (The author has seen gross errors from this).   This practice will cast a bad light on a schedule.  However, summary project administrative activities, e. g. project management, expenses, and accrued costs,  can be individual activities lasting the duration of the project. 

Suggestions for Duration Estimation

A.     Include time for the resource to prepare for the activity

1.      The project manager, superintendent, or discipline leader authorizes the activity to begin.

2.      The assignee gets and studies official project documents, design and specifications.

3.      The assignee may need time to review means and methods with the Project Manager, superintendent, or discipline leader.

4.      The assignee gets tools, software, and the workplace ready for work.


B.     Include time to make the finished activity useful for others

1.      Review the work for quality.  Did the activity meet the objective of its performance? 

2.      Anything learned that affects other parts of the schedule?

3.      Did the activity prove the project is going in the wrong direction?  Sometimes “going back is the quickest way on.” – C. S. Lewis

4.      Provide activities for as-builts and documentation.

5.      Provide activities for technical and management review of the results.

6.      Allow time to report changes and modifications to remaining work.

7.      Notifying supervision that the activity is done.


Calculating duration from estimating libraries

Activity Duration = man-hours * 1 / (No. of Applied Resources) * Efficiency * Degree of Difficulty

A.      Using a spreadsheet or equivalent, break down summary tasks into individual activities.  List in rows in a column.

B.      Place the person-hours and team size from the library into columns aligned with the activity rows.  Adjust person-hours for degree of difficulty and the skill of the resources.  Designate a name responsible for the activity or a generic resource type (like “electrician”).

C.      Efficiency is a number between .1 and 1.0.  It is a judgement.  Consider the workplace and how efficient the resources will be.  Also consider the non-work time needed to prepare and conclude the activity (as described above).  All time devoted to performing the activity would warrant an efficiency = 1.  An example: If the general contractor prescribes all workers to attend a daily safety meeting, set a value between .8 and .9.

D. Microsoft Project (a product of Microsoft Corporation) denotes Efficiency as “Units.”

E.  Microsoft Project will calculate duration if the Task Type is set to “Fixed Work” and the “Effort Driven” checkbox is checked.  This can be set globally in FILE > Options > Schedule, or from the individual activity with TASK > Information > Advanced.

F. The Degree of Difficulty is a factor reflecting how the work differs from the estimating library.


Change Management Considerations

Calculating duration from estimating libraries is easy to prescribe, but is your organization set up for it?


A.      The head of operations should discuss using the estimating libraries for duration determination in a meeting with project managers and estimators.  Develop a short process specification.

B.      Try the method described in this blog on a sample project.  Have those involved present their experience with the project managers and estimators.

C.      Refine and implement the process specification.  Authorize it.

D.     Every year, check how well actual experience agrees with the duration estimates. Improve the estimating library with the new knowledge.

E.      Make sure the estimate used for scheduling is “locked down” and in a folder where people can have read-only access.


Not much in the way of training is required here.  Most people have the capability to set up the simple formula for activity duration in a spreadsheet program.


A detailed project schedule requires a formality in estimating durations. Follow the proven steps in this article to improve the effectiveness of your schedules.


About the author:

Mark Ramsay, PE, PMP, is owner of Effective Project Solutions, LLC.  His past jobs included Project Engineer for DuPont Co., Global Project Manager for Millennium Chemicals, and Project Management Consultant for Johnson Controls, Inc.  Mark graduated from Princeton University with a Mechanical/Aerospace Engineering degree and earned a Masters in Technical Management from Johns Hopkins University.  He is certified in software quality by the ISTQB.  He has won numerous project awards throughout his career, successfully managing sophisticated projects up to $40 million.


About Effective Project Solutions (EPS):

Established in 2012, EPS develops and sells Program Leader task and scheduling software.  EPS also offers scheduling services to clients.  Program Leader is for those operating many small projects who want an alternative to “spreadsheet management” and a replacement for confusing large project software.  Please see for more information.