Unlike activities, activity elements are not scheduled independently. The system calculates the dates for activity elements with reference to the start or finish dates of the activity. If required, you can maintain a time interval for the start and a time interval for the finish in activity elements. The dates of the activity element must always lie entirely within the duration of the higher-level activity.
Requirements Dates of Material Components
If the requirements date is before the finish date of the activity, you can store a corresponding time interval by using an offset to the finish date.
You can also set a requirements date for a material manually, independently of the activity date.
Dates of Milestones
The preceding figure shows a milestone that is assigned to a network activity. The planned date is either entered manually or with reference to the activity. If the date refers to the activity dates, you must decide whether it is to refer to the earliest or latest dates and the start or the end of the activity. Additionally, you enter a positive or negative offset for this reference date.
You can also assign milestones to WBS elements. As of Release 4.6, the planned dates for a milestone can refer to the basic start or finish date of a WBS element.