Hey, I have a few questions if you don't mind I am working 30 hour work week. I recently switched jobs and I consider myself a strong candidate.

In nearly all of my interviews, as soon as I mentioned wishing to work 30 hours (because I want to have time to sharpen my skills in my other 10 hours, which I always sold as a positive feedback loop which helps me be more knowlegable at work), the HR admin/recruiter would go all deer in the headlights, promise to check and get back to me and promptly ghost me.

Luckily I found a place where the CTO appreciated my reasoning. I am just wondering whether my approach was incorrect or whether reduced hours is just really unheard of where I am (southern EU)

I think you're being too honest. I wouldn't blink at any of my employees spending an hour a day at continued education, self improvement, etc. 2 hours a day... Might be pushing it a bit. The 1/he a day is for non-directly work related things that might come up later (i.e., learning network programming or systems or databases, whatever), whereas if you are claiming to make yourself better at your current taskset... There's nothing better than actually DOING that.

Anyway, all that to say that if my employees spent only 35hr/wk being productive with the other 5 for learning, I'd consider that a fine allocation.

Edit: actually not even 35hr, I just can't quite bring myself to support a blanket 2hr a day for this specific non-business productive activity. 35hr/wk of productivity is a bit of a pipe dream

Your mistake was talking to an HR person. They are bureaucrats who understand nothing about our craft and only look for obvious reasons to disqualify you. Your goal is to say as little as possible and get past HR quickly to talk to an actual technical person who can make the appropriate trade-offs. You could be the next Donald Knuth and HR would still reject you for 4-day week because to them you look like [any other shmug + extra burocracy].

Why 30?, that just seems like a strange number.

Assuming 8 hour work days, 32 seems a more obvious choice. You get 1 day/week off.

I've always started at 40, then negotiated down to 36, then to 32 at the same salary whenever offered a raise. If you're having a hard time finding a job, maybe tough it out for a year then negotiate for less hours when you've proven yourself. Obviously helps to be working for smaller companies which tend to be more flexible.

Actually, it seems very logical.

I would do 3 days at 10 hr per day, and 2 days on other stuff. Personally, I would prefer full days slots rather than a few hours free per day

Makes sense to me. 30hrs/week is 6 hours everyday for 5 days

At a guess, I'd say that it's just anything out of the ordinary scares people a bit!

Taking someone on part-time for a traditionally full-time role maybe does involve some additional trust. Maybe a more sustainable approach would be to start full-time, and look at moving to a part-time situation after settling in?

Divulge this after the interview at the offer stage once they've decided they want you. How much you work is a negotiation concern just like salary.

Unfortunately, many companies are very square when it comes to part-time work :-/

If a company said to me were dropping your rate because your part time then I’d be insulted. OTOH hiring is opaque enough that a company could hide that from me and say we’re offering X without letting on they applied a part timer tax.