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My 2 cents on working hours and productivity: if you enjoy and can be productive 70+ hours a week, great! Do it! But I would never ask or expect it of my group members based on science and my own personal experience. 
Many studies show the majority of people can only be productive a certain number of hours (average 45-50) a week. Beyond that, productivity goes down along with life satisfaction. Pop news citation with a link to actual study: https://www.cnbc.com/2015/01/26/working-more-than-50-hours-makes-you-less-productive.html
When people push themselves beyond their limit, they face burnout, general unhappiness, and unproductivity. In my own experience, expecting long hours in and of itself does not result in productivity.
When I was in grad school I worked nights and weekends. It wasn't necessarily expected, but I thought it made me a good, serious, dedicated, grad student. When I started my PD at a national lab, they told me for safety reasons I could only work MF 8:30-5:30.
I scoffed at that - said I was used to working 70 hours a week. How could I get anything done in that time? As it turned out I could, but it took discipline and organization. Mid-day I would start planning my next day so the glovebox would be properly stocked for tomorrow's exp.
My group knows I love Great British Baking Show. That's how I did chemistry. I had a sequence and schedule laid out so I could do multiple exp at a time. It helped being a PD - I had enough experience to know how long everything would take me.
The discipline part was easier. I didn't have a smart phone and I would get regular emails from the lab that they were monitoring my net usage and 'significant time on non-work related sites was a terminal offense'.
Clearly I love social media (and I'm a news junkie) so I now use tools like Rescue Time and putting-my-phone-in-another-room-while-I-work to help me maintain discipline.
The point is, I don't believe grad students and PDs have to work long hours to be productive. But getting enough done requires planning and organization and a lot of introspection on what are the key experiments to move your project forward.
FWIW, I have a senior colleague that does total organic synthesis (a field notorious for long hours) and he told me one of his most productive students ever had a family and only worked 45 hours a week.
So I guess my point is - if you are happy working those long hours, great! But I would never normalize that as the expectation. It would exclude people who could make valuable contributions but can't sustain that lifestyle.
Since this blew I'll add - it will take all of our efforts to make STEM a more inclusive and equitable space. If you want to know how, don't ask your BIPOC colleagues - they have enough on their plate. Instead, follow BIPOC scholars, listen, learn, and act. Suggested follows:
@postdocpapi @DrRubidium @STEMxicanEd @iBJY @DarthScience @doktor_clark @KevinCokley1 @michaelharriot @cesapo @Chem_Diva @cientificolatin @DNLee5 @ravenscimaven @chemist_on_air @TarpehDiem @DrHJHenderson @IshmailSaboor @FutureDrDukes @uche_blackstock @Dr_Dani_AR @BlackInChem
More suggestions for follows are welcome. I've learned SO much from the honesty and uncomfortable truths from these scholars about DEI in STEM and how to work for change.
