For some people this is called breaks.
Yes, you shouldn't do 12 hours full working, you should take sufficient number of breaks in between.
This will fit the 996 system.
In addition, mindlessly repeating experiments isn't a break.
What constitutes a breaks of course different for each person. Maybe some prefer go to gym instead or going for coffee, or simply just strolling around.
Not always true. In the US, you can be required to stay on premises, but it must be paid.
