Since version 7.2.0 you can see the 'Time in Status' of an issue.
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where you can see:
by Status*: how long the issue has been in each state.
by Transition*: how long the issue has been in the state of origin of the transition.
by Assignee*: how long has each user been assigned in each state.
(*All times are displayed on the 24/7 calendar)
How can I see 'Time in Status' of an issue?
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