The 8-hour workday is standard in many industries. Henry Ford calculated that it is an efficient time when a worker can produce a maximum product without losing productivity due to fatigue.

However, now it is the 21st century, and in Ford’s factories mostly robots are working. And many economists are of the opinion that it makes no sense to work 8 hours when the same work can be done in 5-6 hours.

An eight-hour workday still makes sense if people do flow work. But for creative, intellectual work, such an approach is not only ineffective, but even destructive.

Why is the 8-hour workday not suitable for everyone?

The eight-hour workday began as a socialist dream. The author of the idea is considered the textile factory owner and social reformer from Wales, Robert Owen. It was he who in the early nineteenth century called for the introduction of “eight hours of work, eight hours of recovery and eight hours of rest. And it was a far better idea than the 12 or 14-hour workday that was accepted at the time, even for children.

For the next 100 years, U.S. labor unions advocated and pushed for the adoption of the eight-hour standard in various industries. Henry Ford made it mainstream in 1926 by establishing a five-day, 40-hour workweek in his company’s factories. In 1940, Congress officially established the 40-hour workweek in the United States.

There is only one problem these days: It is almost impossible to work eight hours a day in many types of work. Like most people who give mixed opinions and reflections on productivity, I am referring to mental workers–those of us who work at a computer, in an office, or at home. Especially those who create something – writers, programmers and graphic designers.

Frankly, I think eight hours a day is too much for factory, restaurant, call center, or store work as well, and we need to rethink and change that standard in all industries.

I’m a writer working from home, so my schedule is my responsibility. This is both wonderful and terrible. Like many mental workers, at the end of the day I often think, “Where did all those hours go? What did I really get done today?” And unlike people who go to the office, I can’t say: “Oh, I went to the office!” I have no external criteria for productivity, except for the culturally ingrained idea of working eight hours a day, five days a week.

To find out what my time is spent on, and whether I fit into this arbitrary metric invented for criminally exploited 19th century factory workers, I installed RescueTime. Essentially, I spy on myself with the app. It tracks everything I do on my computer and shows me how long I work each day and what I’m actually doing during that time. It’s creepy, but I like it.

I recently had an exceptionally busy and stressful week at work, as I was finishing up a long article for a magazine and writing an urgent news story on a technical topic. Doing both tasks at the same time was definitely too difficult. I felt terrible during those days – depressed, anxious, didn’t eat well and didn’t exercise much – and when that period was over, I got sick right away.

When I looked at the RescueTime stats for those days (Wednesday through Monday), it turned out that a total of 35 hours and 17 minutes were spent on work. I did not rest on the weekend – I worked two hours on Saturday and over seven hours on Sunday. My productivity was high, averaging 84%, but judging by RescueTime’s weekly reports, that’s not prohibitive. (I’m happy to brag that I usually spend less than 30 minutes a day on Twitter, something I never would have guessed before installing RescueTime, and it continues to shock me. I thought Twitter was eating up my days. But no, it’s all about email…)

Even during an unusually busy week for me, I did not work 40 hours. I did not manage to work eight hours a day, although I came close to it a few times, working more than seven hours for three days. Nevertheless, that’s more than I usually do. By comparison, during a routine week in October without major deadlines, I worked 27 hours and 11 minutes at an average productivity of 82%. Normally, according to RescueTime, my time at the computer is 20-30 hours a week (of course, I don’t always work at the computer, but enough to make it a useful metric).

I would feel worse if the other writers in the Slack group I belong to didn’t talk about how much they work. It turns out that no one regularly spends eight hours a day doing this. It’s mostly in the five to six hour range. And until we shared our experiences with each other, everyone secretly felt guilty and lazy.

Many of us in this group are freelancers. But I’m sure if you track the time of mental workers in the office the way I track mine, it’s unlikely you’ll see 40 hours for anyone. Forty hours of availability, yes. Forty hours in the office. Forty hours of thinking about work – at least, and probably more. But how much time do you actually do something, write something, create something? You can’t do that for eight hours a day without breaking down.

This is what productivity guru Cal Newport calls “deep work”. It’s a deep work, which requires total concentration and maximizes one’s intellectual and creative abilities, is vital to many types of activities as well as happiness. After immersing yourself in deep work, you feel satisfaction and pride. But staying in this state of intense concentration for more than three or four hours a day is really difficult.

Therefore, if deep work is the most important part of your activity, but you have an eight-hour workday, you are essentially doomed to spend the remaining four or five hours on outside activities and wandering the Internet.

I’m not saying you don’t need to answer emails, send bills, or conduct interviews at all. I’m not even saying you don’t need to spend time on social media. Every most creative and independent job has an administrative part, and social media is fun, if not taking up your whole life.

But you probably don’t need four or five hours a day for that, do you? So why not just do the deep work, then do the rest, and then finish? It probably takes less than eight hours. And that’s fine. That’s the point.

For me, the ideal creative workday is five hours. An hour to warm up and connect with the team and the world, three hours to focus on a project or maybe two, and an hour to relax, plan for tomorrow, and make sure I haven’t missed anything important. I’m not the only one who thinks this is the best approach to work. Recently in the New York Times, Newport was talking about a startup in Germany that has a strict 8 a.m. to 1 p.m. workday:

To support this new approach, [the head of the company] forces employees in the office to leave their phones in their bags and blocks access to social media. Strict rules reduce time spent in meetings (most of which are limited to 15 minutes or less). Perhaps most importantly, employees now check their work email only twice a day-no lengthy correspondence that takes attention away, no secretly checking incoming messages during dinner or children’s sporting events.

Not surprisingly, you can be more productive in five hours in such an environment than in eight hours in a normal office-if you’re creating something. Of course, there are many important office jobs that can’t be done in five hours alone: human resources, management, even editing, which has much less to do with writing than you might think.

I also wonder how employees feel about the rules. Do they have a chance to get to know their colleagues well enough to feel connected to them, or does everyone just nod to each other during breaks? I wouldn’t want to work in an office where coworkers feel like strangers, no matter how many times I have to check emails.

But for those of us who are engaged in creative, focused, relatively solitary work, five hours is enough. Sometimes more than enough. I take that burden off of you. Go and finally enjoy your day at work.