Working hours depended mostly on how much light there was in the day, so it would vary from ~16 hours a day in the summer to ~8 hours a day in the winter. 

The 150 days per year thing is somewhat debated, depending on the scholar’s views of capitalism vs. their views of medieval serfdom and how one analyzes incomplete information for example, Juliet B. Schor argues:

During one period of unusually high wages (the late fourteenth century), many laborers refused to work “by the year or the half year or by any of the usual terms but only by the day.” And they worked only as many days as were necessary to earn their customary income – which in this case amounted to about 120 days a year, for a probable total of only 1,440 hours annually (this estimate assumes a 12-hour day because the days worked were probably during spring, summer and fall). A thirteenth-century estime finds that whole peasant families did not put in more than 150 days per year on their land. Manorial records from fourteenth-century England indicate an extremely short working year – 175 days – for servile laborers. Later evidence for farmer-miners, a group with control over their worktime, indicates they worked only 180 days a year.

This, along with the many church holidays imposed by the Church, suggests very few working days per year. However, others argue that the records only capture the number of days of labor for one’s feudal landlord, not the full amount of labor needed to maintain one’s own lands or perform the necessary labor of the reproduction of the household. It’s not like animals stop needing to be fed on Day 121 of a calendar year, for example. 

What does seem to be indisputable, though is that the emergence of capitalism – and one of the problems I have with this debate is that there were a lot of stages in between (the commercial revolution, the enclosure movements, the early stages of the Industrial Revolution), so you’re comparing capitalism to a moving target – involved a shift from less regular although occasionally quite intense labor to much more constant labor. E.P Thompson’s work effectively demonstrates how this was bitterly resisted out of a resentment against the discipline involved, that an outside force was telling you when you had to start and stop work – the factory clock, often resisted or challenged by the worker’s watch if they could afford one – or telling you that you couldn’t drink alcohol on shift, whereas before labor had been somewhat more self-directed and self-regulated.