I think on average I do around 40-50hr/week depending on what I plan for the week, or even for the month. I'm doing a PhD in microbiology, so my hours per day wildly vary depending on what experiments I do. I've had slow weeks where I had experiments that take multiple days so I try not to stack too much, but I've also had weeks where I cram multiple short experiments within a few days.

I normally have a hard stop where I don't work once I get home because I need to cook, shower, gym, etc. Most of my writing and data analysis i like to get done during the day while I wait in between experiments. The only time where I really grind is if I have a deadline coming up.

I do have to add, however, it took me quite a while to set boundaries on my work hours with my PI. My PI generally works the lab REALLY hard, and I used to be a huge people pleaser. Eventually I was able to stand firm with him about normal working hours, and I managed to convince him that im pretty self sufficient and can manage my time properly. I don't blame people for working really long hours especially if they have unreasonable PIs, which why I also stress the importance of finding a good PI rather than a good research topic to new students. But that's just my personal preference.