Project phases with timeline:
  1. Concept and brainstorm phase - 1 week.
  2. Initial user flows and mockups - 1 week.
  3. Developer/Engineer sanity check and discussion - 1 hour (or more if needed).
  4. Initial spec and user stories, user test design. - 1 week.
  5. User test working prototypes - 2 weeks (depending on complexity).
  6. Initial user testing - 3 days.
  7. Interpretation and data presentation - 2 days.
  8. Spec, mock, and prototype revision, additional test design - 1 week.
  9. Secondary user testing for revised features - 3 days.
  10. Interpretation and data presentation - 2 days.
  11. Final revisions to spec, mocks and user flows - 1 week.
  12. Detailed technical review, spec review. Technical revisions. 1-5 days.
  13. 2 week buffer for initial prototypes, spec negotiation, or possible retesting for tricky elements.

Notes:
  • This assumes an ideal and focused timeline. In reality scheduling and other projects would probably require modification. Each scenario or independent feature set could be broken up with a cascading schedule for prototyping and testing to better fit with particular timeline needs.