I like my regular f/t job as well, especially since I get moved within the company ever six to twelve months. It has given me a lot of freedom to do things that won't show a profit instantly like write and get some accounting qualifications.

However looking at what I really want to achieve I have decided that a startup is the way to go for me. Exit planned for September. Unfortunately it's not something I could run concurrently with a full time job, or else I might launch earlier to reduce risk :)

To answer the original question: Specs, use cases and UI mock-ups were 12 hours a week for 3 months. I wrote the first prototype this weekend (60 hours), so now I will be doing increments towards a stable production version, planned 12 hours per week.