Long story short; with 5 developers I created and deploy into production a web application platform with web mobile and native iOS & Android clients in… 8 weeks.
First I start to work with the product ownership team. They were lost but after 2 weeks I could make a minimum viable product I can develop in the 6 weeks I had after. In between the development team was working on CRC cards, SOW and work on a paper with sharped features for the application.
In the first 2 weeks we develop the model and business logic with the wireframe version of the web application.
The next 2 weeks we made all the flows including the deployment on a staging server.
The last 2 weeks we fix all the bugs, create the API REST with JSON and the 2 native clients for iOS and Android.
Insane, but it work.