Project duration entails the probable time it would take to complete a given project. Accurate assignment of project duration is very important because it affects the overall cost or expenditures involved in the project.
Two types of expenditures are usually encountered in every project. These are capital expenditures and recurrent expenditures. Capital expenditures are expenditures made in the creation of fixed assets and on the acquisition of land, buildings, and intangible assets. Recurrent expenditures on the other hand are expenditures made on operations, payment of wages and salaries to unskilled and skilled labour force, purchases of goods and services, and current grants and subsidies. It also includes expenditures lost due to idle time of equipment such as during holidays or unprecedented delays, and expenditures incurred in hiring equipment.
The duration of the project does not significantly affect capital expenditure but this is not the case with recurrent expenditure. The longer the project is delayed, the more the recurrent expenditure. For instance if one is not working for say 3 months and he has 30 staff strength, he would continue to pay the staff for the three months without progress in the job.
The effort to reduce recurrent expenditure to the barest minimum necessitates the need for construction planning/project scheduling before the commencement of the project. Through construction planning, adequate duration, known as elapsed time (te) is assigned to each event or item in a project, and studies are done to know what challenges could be encountered during the execution of the project and how to mitigate these challenges.
To assign proper duration to a given event in a project, three distinct time estimates are usually considered. These are:
An optimistic time, a
A most likely time, m and
A pessimistic time, b
We know the definition of an optimist as someone who is hopeful and confident about the future or the success of something. It is an extreme side of human personality. An optimist may not factor properly the inevitable hitches that could come up in a project because of his overt positive mindset. The pessimist who is the opposite of an optimist may factor more than expected hitches in a project because of his mindset. The most likely time comes between the optimistic time and the pessimistic time to smoothen the extremes of these two times however, it may not still give the required duration. Thus, these three times are usually incorporated in assigning duration to a given event in a project to get the most feasible duration (elapsed time) for the project.
It is worth noting that these estimates can be obtained from individuals who have carried out similar projects in the past or are familiar with such activities. They are usually stated in days, weeks, and months and are not altered unless a significant change takes place in the scope of the work or the assignment of resources. The single estimate of time required to complete the project can be determined as follows:
te = (a + 4m + b)/6
If the optimistic time to complete an event project is 4 days, the most likely time is 8 days and the pessimistic time is 11 days, determine the elapsed time estimate required for the event.
te = (4 + (4 x 8) + 11)/6 = 7.8 days which is approximately 8 days
Having determined the total event required in the project and the duration required for each event, these are cumulated to determine the total duration for the project. The duration for each event would be used to develop a network activity chart or Gantt chart to guide the progress of the work.