To set an exact (absolute) start date:
- Key moment: click on the key moment in the Planning window and in the Details pane make sure that the bottom option is checked (‘At this exact date’). Then use the date selector to set the date of the key moment.
- Activity: click on the activity in the Planning window. Select the Duration tab if it's not visible in the Details pane. Make sure that the bottom option is checked (‘At this exact date’). Then use the date selector to set the date of the Activity.