I've been doing devops contracting for a startup at 25 hours/week lately. I'm digging it a lot, because it gives me two days during the work week to go outside and plenty of time to work on my own stuff. I don't feel guilty when I go home after one of those work days and don't put time in on one of my projects. That's a powerful thing.

(Shameless plug: one of my arrangements is ending soon and I'll be taking on more devops and automation work; at every place I've been I've added pretty big multipliers to engineering output in a fairly short amount of time, and my email's in my profile if that appeals to you.)

I work in a Teradata shop in a major financial institution and the hours are reasonable and the work is borderline relaxing. There is a nice middle ground between 20h/wk and the startup meatgrinder if you seek it.

I play poker professionally so I get to set my own hours.