It's very uncommon to go in that late. What's much more common is people taking morning meetings from home and then going into the office to complete their day. If you're a 996 grindset blogger, I suspect you're fairly likely to mistake one for the other.
They work a lot of days (they have very few paid leaves compared to EU in general) but not a lot of hours per day (from what I could see working at French/American companies)