I seem to be alone in this, but I actually do about 25-30 hours of actual programming work each week. And that's sit-down-and-concentrate-and-build-shit work. I'm pretty ruthless about declining extraneous meetings and I keep my door closed most of the time.

I think it's reasonable to have 25% of a 40-hour week be for meetings, helping other people, eating lunch, sitting in on interviews, and learning/trying out new things.

And yeah, 25-30 hours is probably a maximum, and it needs to be done in three-hour chunks at a minimum. As a manager you can easily destroy that by allowing an environment where a solid three-hour block of time never happens for a dev.