In Structure.Gantt, duration for each task can be calculated in one of four ways:

Automatically

By default, task durations are calculated automatically, based on each task's work estimate, the calendar, resource availability and the Work Estimates settings.

To adjust the duration of these tasks:

Dragging the right side of a task bar will cause the task's work to be updated and its duration to be recalculated.

Based on Start and Finish Dates

When tasks are manually scheduled and have both a manual Start and Finish Date, the task has a fixed duration, spanning the time between its Start Date and Finish Date.

To adjust the duration of a fixed duration task, drag either side of the task bar. This will update the task's Start or Finish Date, and the duration will be adjusted accordingly.

Adjusting the duration of a fixed duration task does not affect its work estimate.

Based on Sprints

When tasks are scheduled based on sprints, they have a fixed duration corresponding to the length of the sprint. It is not possible to adjust the duration of these tasks, except by removing them from sprint-based scheduling or changing your sprint duration settings.

Manually Setting Fixed Duration

You can set a fixed duration for an individual task by updating the Fix. Duration field in the Task Details Panel.

Tasks can also be assigned a fixed duration based on a Jira field or formula, by assigning a Fixed Duration Attribute in the Gantt Configuration.