Hi Justin,

The instance history data is stored in Forms database table [cf_bp_worker_instance_history] and [cf_bp_worker_instances]. 

Following is a simple SQL query I developed to query the start date of start step and finish date of a specified step given step ids and process name, that you may start to build report with

--update process_name, start_step_id, task_step_id variable value before use

declare @PROCESSNAME nvarchar(50) = 'process_name'
declare @STARTSTEPID int = start_step_id
declare @TASKSTEPID int = task_step_id

SELECT T2.bp_instance_id, MIN(T1.start_date) AS start_date, MAX(T1.finish_date) AS task_finish_date
FROM cf_bp_worker_instance_history T1
INNER JOIN cf_bp_worker_instances T2
ON T1.instance_id = T2.instance_id AND T2.bp_instance_id IN
	(SELECT bp_instance_id
	 FROM cf_bp_main_instances
	 WHERE bp_name = @PROCESSNAME)
WHERE step_id = @STARTSTEPID OR step_id = @TASKSTEPID
GROUP BY bp_instance_id
ORDER BY bp_instance_id