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In time management, timeboxing allocates a fixed time period, called a time box, to each planned activity. Several project management approaches use timeboxing. It is also used for individual use to address personal tasks in a smaller time frame. It often involves having deliverables and deadlines, which will improve the productivity of the user.
|-- Mary Poppendieck , Leading Lean Software Development|
Timeboxing is used as a project planning technique. The schedule is divided into a number of separate time periods (timeboxes), with each part having its own deliverables, deadline and budget.
In project management, the triple constraints are time (sometimes schedule), cost (sometimes budget), and scope (sometimes performance).Quality is often added, sometimes replacing cost. Changing one constraint will probably impact the rest.
Without timeboxing, projects usually work to a fixed scope, such that when it is clear that some deliverables cannot be completed, either the deadline slips (to allow more time) or more people are involved (to do more in the same time). Usually both happen, delivery is late, costs go up, and often quality suffers (as per The Mythical Man-Month principle).
With timeboxing, the deadline is fixed, but the scope may be reduced. This focuses work on the most important deliverables. For this reason, timeboxing depends on the prioritisation (with the MoSCoW method for example) of deliverables, to ensure that it is the project stakeholders who determine the important deliverables rather than software developers.
Timeboxes are used as a form of risk management, to explicitly identify uncertain task/time relationships, i.e., work that may easily extend past its deadline. Time constraints are often a primary driver in planning and should not be changed without considering project or sub-project critical paths. That is, it's usually important to meet deadlines. Risk factors for missed deadlines can include complications upstream of the project, planning errors within the project, team-related issues, or faulty execution of the plan. Upstream issues might include changes in project mission or backing/support from management. A common planning error is inadequate task breakdown, which can lead to underestimation of the time required to perform the work. Team-related issues can include trouble with inter-team communication; lack of experience or required cross-functionality; lack of commitment/drive/motivation (i.e. poor team building and management).
To stay on deadline, the following actions against the triple constraints are commonly evaluated:
Many successful software development projects use timeboxing, especially smaller ones. Adopting timeboxing more than tripled developer productivity at DuPont in the '80s. In some cases, applications were completely delivered within the time estimated to complete just a specification. However, Steve McConnell argues that not every product is suitable and that timeboxing should only be used after the customer agrees to cut features, not quality. There is little evidence for strong adoption amongst the largest class of projects.
Timeboxing has been adopted by some notable software development methodologies:
Agile software development advocates moving from plan driven to value driven development. Quality and time are fixed but flexibility allowed in scope. Delivering the most important features first leads to an earlier return on investment than the waterfall model.
A lack of detailed specifications typically is the result of a lack of time, or the lack of knowledge of the desired end result (solution). In many types of projects, and especially in software engineering, analyzing and defining all requirements and specifications before the start of the realization phase is impossible. Timeboxing can be a favorable type of contracting for projects in which the deadline is the most critical aspect and when not all requirements are completely specified up front.
Individuals can use timeboxing for personal tasks, as well. This technique utilizes a reduced scale of time (e.g., thirty minutes instead of a week) and deliverables (e.g., chores instead of a component of a business project). Personal timeboxing is said to help curb perfectionist tendencies (by setting a firm time and not overcommitting to a task). It is also suggested that personal time boxing can create an increased pressure for an individual which will lead to better creativity and focus towards a task. 
Timeboxing acts as a building block in other personal time management methods:
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