I work 24h/w (TWT) for my employer. I did this by... saying that's what I could do when they offered me the job. (There are some specific personal circumstances that prevent me from taking full time work.) And sure, it does limit you; a lot of places demur, but not everyone. For sure my small company are happy to have me. Of course they are: they get a massive bargain. I am prorata so they get a developer for janitor wages and still everything gets done. Who wouldn't be happy with that deal?