This only works when you divide the time spent working over the year. As a medival peasant you worked your ass off in spring or whenever you sow your fields, kept it up while it grew, which was somewhat normal working times by todays standard, and toiled for double digit hours in harvesting season again. After that was time to do literally nothing. When you look at seasonal holidays in many european countries, they are mostly at the end of harvesting seasons, when you could easily be blackout drunk for a week because there was nothing else to be done. I personally don't mind regular working hours when the alternative is half a year of 15 hour shifts and half a year of more or less no work.