"I could definitely have improved it significantly with 6 hours. But I don't believe anyone, applying for an e-commerce programming job at a major online retailer, would have done significantly better with 4 hours, this leads me to conclude that people are maybe doing 6 hours or more."

I've done many coding tasks over the years and I never limited myself to 4 hours. This is to showcase your abilities. Make it the best you possibly can, without over-engineering it. I think only once did I not get the job.

"Has this amount of time gone up in recent years? Or in the last few months due to the economy."

No, but you didn't get the job, so you need to do better.

"I'm also wondering, and here it may you want to just send me messages privately on this, but are you married and has marriage/kids affected your time on programming assignments (as I am thinking about particular legal challenges, in an EU context, to the legality of programming assignments - if it turns out I have to spend 8 hours per assignment nowadays I'd rather mount a legal challenge)"

A legal challenge? I would never hire you. Good luck.

Generally my personal rule is: don't do it.

Here are my rules for accepting coding assignments:

* See the grading criteria along with, or before, the coding assignment instructions. Otherwise, its subjective bullshit that can fail for any reason. Worse, there is a small yet common probability of this being unpaid labor for their actual work product.

* Make it known to them that you will store your answer in public without their instructions or work materials. If that is a deal breaker then there is a trust/honesty problem. This is your time without compensation.

* As for time and duration of total effort this should vary due to the complexity of the assignment and your level of interest. Since there are no obligations here the minimum time is 0. You can always walk away. If you find the assignment fun or interesting take as much time as you want and later use the answer in your personal software if you can.

My experience doing these, as a former JavaScript developer, leads me to believe this isn't a measure of the applicant's abilities but rather a measure of the evaluating developers, the employees, comfort in your coding style. That being said don't do the assignment in the most precise or performant way unless the instructions say otherwise. Do it in the most common and popular way according to an extremely junior developer even if much slower and much larger, and also don't be shy about including too many popular dependencies.

If I were to get a "coding assignment", I would tell them 'no'

So I would spend 0 minutes

And not just because I am not especially close to a 'coding' or 'developer' role in my IT career

But because they are all* a complete and utter waste of time

Unless you mean a whiteboarding session in an in-person interview, where you see approaches to problem solving, swags in the direction of an answer, refinement of the problem statement, etc - those I spend 15-20m on (out of the 45-60m interview session)

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* maybe there is a coding assignment that is not a waste of time, but I have never in my well over 20 years in IT seen it

Personally, I just won't do those sorts of large assignments. I take the request as a signal that I wouldn't be happy working at that place. Short tasks meant to be done during the actual interview are fine, and I have plenty of existing code that potential employers can look at.