Slack Time and Critical Path

• Slack Time

  • Available Time - Estimated (“Real”) Time for a task or activity
  • Or: Latest Start Time - Earliest Start Time

• Critical Path

  • The path in a project plan for which the slack time at each task is zero.

The critical path has no margin for error when performing the tasks (activities) along its route.

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Slack time is a measure of how much we can goof off without causing major troubles for the project. If a task has no slack time, it means it has to be done immediately at the indicated start time.

For example, surveying can start on day 1, so its earliest start time is day 1. However, because it takes 15 days to request and receive permits, surveying can begin as late as day 13 and still not hold up the project schedule.