Many companies in my area have a minimum five day work week, with a sixth day of work pretty much implied/required for anybody looking to get ahead. This is in response to the market more than anything else. So, if you're interested in making over $150k - which is pretty much the minimum amount needed to own a home and accumulate savings/investments in my region of the US - then you can expect to be working 5.5 to 6.5 days a week (8-12 hours a day). If you're not interested, there is a line of people a kilometer long willing to take your place. And your boss knows that better than anybody.

A four day work week would be awesome, but I'm not sure how long I'd last working 15 hour days. I once worked a job in the creative field that required 100 hour weeks. That sucked, and I didn't last more than 1 1/2 years. Someone else quickly swooped in and grabbed my job same day. There are countless hoards of Americans willing to work and do nothing else. They're addicted to it. They love it.