With the decomposition of the deliverables into the WBS and further into activities, and the estimation of the resources required to complete those activities, we can estimate the activity durations.
Frequently we’ll use analogous estimation, picking up the initial estimated durations from previous projects. These can be reviewed against the current scope and the resource estimates to narrow the estimated durations. As each estimate is firmed and the updates are made, the project management software will aggregate up to the higher work package levels and we will need to review the overall estimates duration to ensure that it looks reasonable. Frequently, the activity durations will be influenced by the deliverable milestones – working backwards from the execution start dates gives us blocks of time within which (or before which) the preparation activities need to be completed.
Activity durations may be influenced by the choice or availability of resources and any risks or constraints previously identified, and should be as accurate as you can make them – any contingency or buffer will be added in as a separate “activity”.
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