To define how much time will be required to complete a project, it is necessary to provide:
- Initial duration estimates for the individual activities/tasks in the project (these will be refined once resources are assigned and availability is known)
- Logical relationships/dependencies between tasks (predecessors and successors)
- Any lead/lag time in those relationships, to create intentional overlaps or delays, respectively.
- Any task start/finish constraints, such as SNET (Start No Earlier Than), FNLT (Finish No Later Than), etc.
Usually, an initial duration is entered for each activity/task, and then, once resources are assigned and effort is estimated in detail, the task duration may be refined accordingly (based on the estimated effort and the resource's availability).
The purpose of adding the initial duration estimate is to determine at a high level when resources must be scheduled and when the project will complete. The duration of the work can be graphically represented on the Gantt chart (by the length of the line) and/or as a WBS column. The Gantt chart serves as a significant aid in visualizing the schedule as logical relationships are created. The initial duration estimate should represent the best case schedule before factoring in other impacts.
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