Who are the users? What are the primary user tasks that align with business goals? This is where we work together on the problem to identify industry gaps and opportunities (whether your "cool idea" is really cool enough for you to continue pursuing).

Mindmaps I use: WHO-DO-BE-FEEL (Empathy Map), Lean Canvas (for start-ups), User Storyboard, any existing brain-storming gems from your mind

Timeline: 1-2 weeks, with up to 2 team revisions (unlimited if this is part of an on-going product design service).