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Tasks, Duration, and Structure

The building blocks of every project schedule.

Task vs. Activity: A Note on Terminology

In formal project management literature, an activity is a discrete piece of work that consumes time and resources. It has a clear beginning and end. The term is precise and unambiguous.

In practice, most people say "task". Tools use "task". Conversations use "task". We'll use both terms interchangeably in this book, as a competent project manager should be comfortable with either.

Pro tip: When reading PM textbooks or preparing for certifications (PMP, PRINCE2), expect "activity". When talking to your team, expect "task".

Understanding Duration

Definition: Duration

The time required to complete a task. This is work time, not calendar time. A 16-hour task takes two 8-hour workdays — but might span three calendar days if there's a weekend in between.

Duration is your best estimate of how long the work takes under normal conditions. It should be:

  • •Realistic — based on experience, not hope
  • •Inclusive — accounting for review cycles, handoffs, minor rework
  • •Not padded — buffer should be explicit, not hidden in estimates

Related Terms

Effort (Work)

The total person-hours required. A 40-hour effort task might have a 5-day duration if one person works on it, or a 1-day duration if five people work in parallel.

Milestone

A zero-duration marker representing an instant in time. "Contract signed", "Phase 1 complete". Milestones mark achievements, not work.

Summary Task (Parent Task)

A task that groups child tasks. Its duration is calculated from its children. Also called a "hammock" or "summary activity".

Constrained vs. Unconstrained Activities

This is a crucial tactical distinction. Every activity in your schedule is either constrained or unconstrained — and knowing which is which reveals where you have flexibility.

Constrained Activities

Activities that must happen at specific times or in specific sequence. Their timing is driven by dependencies or date constraints. Delaying them delays the project.

Unconstrained Activities

Activities with flexibility in their timing. They could happen earlier or later without affecting the project end date. This flexibility is called float or slack.

Understanding this distinction is fundamental. In Chapter 3, we'll explore how to identify which activities are constrained — and how that leads us to the critical path.

Structuring Work for Clarity

Good structure makes schedules readable and manageable:

  • Use hierarchy: Group related tasks under summary tasks. "Phase 1 → Design → Create wireframes".
  • Keep tasks atomic: Each task should represent one logical piece of work. If it has natural phases, split it.
  • Make waiting explicit: Don't hide delays. If there's a 2-week permit wait, create a task: "Wait for permit approval (10d)".

Chapter Summary

  • • "Activity" is precise; "task" is common. Know both.
  • • Duration is work time, not calendar time.
  • • Activities are either constrained (fixed timing) or unconstrained (flexible).
  • • Good structure uses hierarchy, atomic tasks, and explicit waiting activities.
Chapter 1Chapter 3: The Critical Path