I've worked 20h weeks for the past 18 months. It's been great. I actually wanted to do 24h but they said they only allowed 75% and 50% part time. I was wondering how it would work to do a 4h day but it's actually a nice way to soft-start the "weekend".
As for how I negotiated it, I just told my manager I wanted to do it. He was like "well, if it's that or lose you, sure." Part time is not very common where I work, so approval had to go up to VP level but was not a problem. I'm paid 50% of what I was paid before, I didn't feel the need to negotiate this. Full benefits.
My nominal work week is 8h+8h+4h, but when we've had deadlines I've also done 4 full weeks and them 4 weeks off. Both have their advantages and disadvantages.
As for how I negotiated it, I just told my manager I wanted to do it. He was like "well, if it's that or lose you, sure." Part time is not very common where I work, so approval had to go up to VP level but was not a problem. I'm paid 50% of what I was paid before, I didn't feel the need to negotiate this. Full benefits.
My nominal work week is 8h+8h+4h, but when we've had deadlines I've also done 4 full weeks and them 4 weeks off. Both have their advantages and disadvantages.