You could do it all in a morning if you didn't do any of the following:
- Create and implement a high fidelity design.
- Include the project-specific requirements that every feature has... the auth system needs to work via ajax, connect with a legacy db, and include animated transitions. Private messaging needs responsive design and realtime updates. Etc. etc. etc.
- Deal with scope creep, clarifications of the specs, and hours of related discussions.
- Write automated tests.
- Do live QA.
- Fix inevitable bugs, browser and device inconsistencies, ux problems, etc. etc. etc.
- System administration and deployment.
- Load testing, caching, performance tuning.
If a client tried to tell me I should be able to do all this in a morning, I'd fire THEM on the spot.