The feature is enabled by setting Planner.IndicateNonVisibleItems = true. The indicators are automatically displayed and updated when items are created or when the planner grid is scrolled. Whenever items are programmatically created, an update of the non visible item indicators can be forced with: Planner.UpdateNVI;

Example:

with Planner.CreateItem do 
begin 
  itembegin := 33; 
  itemend := 37; 
  completiondisplay := cdHorizontal; 
  completion := 80; 
end; 
Planner.UpdateNVI;