Working for over a decade in silicon valley, I have yet to come across a company or group where the majority opinion has been that people must work more than 8 hours a day to succeed. I'm not sure if there ever was a time when overworking was a norm in the industry, but it definitely has not been the case for a while.
Heck multiple companies, including Amazon, are starting to experiment with 4 day work weeks. If you are in a position where you must justify (to yourself, management, or the public) a regular work schedule, save your energy and just quit.