Why am I not able to edit some fields such as Planned Cost Start and Finish on the Idea Creation Page?
Release: 451-101-15.3-Clarity-Creator User License
Having these fields non-editable on the Idea Creation page is by design.
However, once you create the Idea, you should be able to edit the fields.
Once you create a Cost Plan which is the Plan of Record for the Idea, the start and finish date gets populated automatically to match the Plan of Record and once again become non - editable.