While in timeline view of either Idea, Project, Custom Investment you cannot select the blueprint on the timeline view.
When you click on the field to select the blueprint the box does not change to dropdown and it is blank, nor can you enter any values.
You can select the blueprint in the flyout for your investment or enter on the grid view.
Release :16.0.3 and prior
The functionality was changed in 16.1 and future releases to have the blueprint attribute show the options on the timeline.