Measure about when an issue was assigned

I’m looking for a measure about WHEN an ISSUE transitioned from UNASSIGNED to having an ASSIGNEE (doesn’t matter who the assignee is).

I’m doing a bar/gantt chart with the following data:

  • Issue created date (predefined measure)
    [Issue].CurrentHierarchyMember.get(‘Created at’)
    - DRAFT to TO DO Date (Defined measure)
    ** ([Transition].[Draft => To Do],[Measures].[Transition to status last date])**
  • IN PROGRESS Date (Defined measure)
    ([Transition].[To Do => In Progress],[Measures].[Transition to status last date])
  • DONE Date (Defined measure)
    ([Transition].[In Progress => Done],[Measures].[Transition to status last date])

I want to replace the DRAFT to TO DO with the measure I’m looking for.