For example, in today's society we do not think of basic chores like laundry as work, but in the past laundry was far more labor-intensive due to the lack of washing machines. Is repairing your broken furniture or clothes work? Is preparing your own food work? Those things are trivialized in today's advanced capitalist societies, but might have been a substantial part of life for people in the past. Nowadays most people seem to just buy new furniture and clothes, and even food preparing has been substantially trivialized by resteraunts, orders, takeouts, and readymade meals, so we're probably much more prilvileged than they were. But did the medieval people saw all of this extra work as "work" in today's sense? (Graeber's famous book ("Bullshit Jobs") kinda touches on this aspect in the end chapter, but I wish he've delved a bit more on it. There's a whole anthropology of work that's left unexplored...)
I just think that even the conception of work itself might have been too different to compare medieval society's work hours to today's. We in modern societies are too accustomed with wage labor, to even imagine that these people might not have even thought about tracking the hours they were "working".