The “Workflow Duration” value in the Workflow Heatmap does not show past executions. For exemple, when checking a workflow at a different time within the same day, the Workflow duration value will stay the same regardless of which execution time is chosen.
This behavior is by design; this value will only be filled with the last execution duration of the workflow for a particular day; there is no historization of that data. When selecting a different day, the Workflow Duration will change but will only show the last execution duration for that day.