I can't upvote you more than once, so I'll add an "amen" and a personal experience.
A while back a company where I'd been doing contract web dev work had a dual account/project management role come open and offered it to me. I'd done some client-facing work for them before and freelancing on my own, so I thought "How hard could it be?"
Two things I didn't know when I said yes:
* how much work there was for the small team in place -- and because I wasn't replaced as a technical resource, the team had just gotten smaller
* how different development and management work are in terms of headspace. It's very hard to do both simultaneously, because one job requires a lot of immersive concentration, and the other requires near continuous back-and-forth to discuss, track, and push a lot little pieces of information where they need to go.
So... I'd end up having to find non-office hours to do development work, but still had to be "on" and available during normal office hours.
I managed to keep it up for about six months. Kindof. Wouldn't recommend it, though.