End Dates (and not Due Dates) should be computed from Start time (which could be dependent on another task) and lapse time. Ellapse Time is the effective time to do a task if the person is 100% on the task. But because of meetings, etc., we know that the real-time would be different. So, we should be able to enter a percentage of elapsed time that is Effective time. Then, Elapsed time would be computed from % of Effective time and vacation time when the tasks are scheduled to happen.