I wouldn't be at all surprised to find out that the number of companies started as lifestyle businesses, freelancing, etc. far outweigh what we think of as "startups" here. Many of them are very explicitly targeting number of hours - I know a bunch of people who went freelance mostly because they can target 30h/wk that way a lot more easily than in traditional employment.
I have no numbers but what I've seen from people owning businesses with employees (or even alone) in various fields none are stopping at 40 hours a week. That is in Sweden.
EDIT: Just for fun I googled some and found an article where they had made a poll in a magazine about small business owners. The distribution was:
Less than 30h 7,5% 31-35h 2,3% 36-40h 6,5% 41-45h 10,5% 46-50h 14,9% 51-55h 13,9% 56-60h 15,8% 61-65h 8,0% 66-70h 7,1% 71-75h 3,4% 76-80h 3,9% More than 80h 6,2%
https://www.foretagande.se/nyheter/sa-manga-timmar-jobbar-eg...
Yes of course, but I did not mean to do that. I don't know what the relative distribution is, but think HN readership plausibly has a particular view of "starting a company" which is not very reflective of that distribution...