It would depend on the industry, and it would also be effected by seasons. In general, if you were a peasant and a man (or boy) you were up at dawn and working all day with breaks for meals. At nightfall you were mostly forced to stop working so that gives you the range for a work day.

As a farmer, to survive, you're probably at work all day (still the case for farmers until the last century). Women were at work all day taking care of the house, preparing meals, mending, sewing and making clothes, and when needed, helping the men in the fields. In my family, I was told that my great-great-grandmother baked a dozen loaves of bread PER DAY for her family of 11. Obviously this requires access to that much food, but gives you perspective on the work involved in running a big household like that. Think about it: if you have a smaller family- say 6 children and a husband to take care of, that's still a lot of food to make, a lot of clothes to clean/mend/make and your house to maintain.

Certain times of year would certainly be busier - the spring and fall would have to be the worst : planting, harvesting, and preparing for winter. Once winter came around, work was decreased, but they still worked. They probably took this time to do inside work like making tools, repairing the house/barn/fences, etc. and the year round upkeep of any animals. Keep in mind the light problem- when the sun goes down, the work (mostly) stops so that means less work in the winter.

Religion was a huge part of medieval life, serving as a source of social interaction, guidance and control. You were expected to be at church on Sunday - and during some seasons, more than just weekly (sometimes daily). Once you were home, back to work. Just because it's Sunday doesn't mean your cow doesn't have to be fed and milked. And if there's a broken fence, it's getting fixed whether it's Sunday or not. In terms of festivals and feasts, you would have to organize your work around them- just like we would today. And most of those festivals were related to times of year - particularly farming times of year. Many places had a "planting season" festival or spring festival - so you'd have to have ploughed and prepped the fields before that to be on time to plant. Harvest festivals would either mark the beginning or the end of the harvest. Although there were many festivals and they served to break up the work, provide some social interaction and fun, work always needed to get done.

In terms of work, we can take quite a lot of it as humans as long as we're taken care of health-wise. I think more of the problem was lack of sanitation, medicine, and most of the time, a low-quality diet.