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By default the WBS Gantt is enabled by default, when it is accessed for the first time the current hierarchy in Timeline will be copied and assigned the Work-Breakdown-Structure (WBS) number accordingly. The changes afterward will be maintain in the WBS order and not synced with Jira Issue hierarchy TImeline. WBS Gantt can be disabled by Jira admin or the board admin.
Go to Board Settings → Features
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You can select to enable which feature on the board, Timeline and WBS Gantt both can be available together but to avoid confusion we recommend using only 1 on your board.
WBS Gantt Menu
Menu
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Full-screen mode: click on the button to maximize the Timeline view to full screen
Today button: click on it to move the timeline focus to the current day.
View mode: you can select Weeks, Months or Quarters view
Refresh: retrieve the latest data and update the timeline in case you don’t want to refresh the whole page
View settings: customize the display of the timeline