A user calendar always has the highest precedence. When a user calendar is available, any due date calculation for that user always considers the user calendar.
When an activity workstep has a single performer, then the due date for the workstep and workitem is calculated using that individual user's calendar, if available; otherwise, it is calculated using the system calendar.
When an activity workstep has multiple performers (a group or a queue), and the workstep is marked as 'perform by any member', then both, the workstep instance's and work item's, due dates are calculated using the system calendar.
When an activity workstep has multiple performers (a group or a queue) and the workstep is marked as 'perform by all members', then the due date for individual work items is calculated using individual user`s calendar, if available; otherwise, it is calculated using the system calendar.
When there is no system calendar, the BP Server calculates the due date by adding the duration to the workstep instance activation time.
