Is it actually just "a bit more time"? I can only go by what I hear from others, but the stories I read in HN comments make it sound like that "bit more" is at least half-time work.
When I was freelancing, 35-40 hours per week, it was quite often that I only got to spend 10 hours a week doing actually programing. Anything over 20 was amazing.
You are forgetting, that if you spend 20 hours/week on your own business, then you would spend most of these 20 hours thinking and only ~5 hours/week coding.
Which would probably move your business forward very slowly.
