You could, but that is a very big brass ring to put in front of your employees. If you are working that many hours there better be a good reason, like a big payday. Startups are different than PMEs because the only way you would even think about working 60+ hours is if you have some equity in the success of the company.

There are 2 ways the 35 hour week works:

1) You are paid for 35 hours/wk and work as much as you want all year long. December arrives and you go full RTT. You basically take a vacation while the company pays you the balance of those over 35 hour weeks. I've been in a few places where half the office is gone for the entire month of December, and sometimes November. If you don't use all your RTT by 31/12 you've basically worked for free.

2) Overtime. In my case my CDI (employee contract) is for 35 hours + 4 overtime hours that I've agreed to. Say the company only wants me to work 35hours/wk one month, too bad pay me 35+4. And if I go over 39 hours? RTT. Depending on the workplace, this can either get collegial or hostile very quickly.

Also, when it's 7-8 hours of work the french really do work those hours. This is in contrast to my American observation of working 6-7 and goofing off for 2-3. But then you're always having to stay late. This pacing requires proper project management, something that was really lacking in most of my american bosses (Americans tend to inherit the manager job, to go cadre in France you actually have to take courses on managing people).

And then there's the typical programmer under the SYNTEC union convention, who is paid for 37.5 hours/wk, with only 10 days off for RTT per year.

But in reality, we work the full 39/40 hours, because we're paid by the day, and there's much work do be done anyway. So, we're averaging 35 hours on paper, but more like 37.5 in reality.

I guess that's just something to keep in mind while negotiating the salary.