Duration is the time period that is required to complete a task or an activity. It is expressed in units of time - hours, days, weeks, months or years.
What for do we need to know the duration?
We need to know the duration of a task or an activity, so we are able to plan (planning) and manage task (task management). If we know the deadline, then we can use the duration to determine when exactly we need to start the activity or to start working on the task. For example, if we know that an activity takes a month and we need to finish it by the end of the year, we need to start working on it at the latest on December 1, or, given the holidays, we need to start even earlier just to make sure. This implies that when planning and estimating the duration, it is also necessary to take into account the periods of time when the task cannot be worked on (e.g. public holidays).
The duration can also be used when planning in the other way around - if we know when we can start working on the task, then we can determine by when it can be done.
When planning projects, that is to say a set of different tasks or activities that are linked together, we need to use methods to help calculate the total duration (e.g. Critical Path Method (CPM) you can also compute and visualize (eg Gantt Chart).
The duration is expressed in time units - hours, days, weeks, months, years.
What is the difference between duration and effort?
Duration tells you how long it will take to complete a task or activity. On the other hand, effort tells you the amount of time that we need to spend on it. Therefore, the duration of 1 month doesn’t say anything about how much time the task or activity actually takes - it may require, for example, only 1 hour a day of only one worker, but it may also require 10 full-time employees to work on it throughout the month.