I ran a second batch through the hot air popper this evening. The first batch cooked for 25 minutes, and it was a bit lighter than I'd have liked, so I let this one run for 35 minutes. My inexpert eye puts this at about a full city roast, with the first slight sheen of oil showing on the outside of the beans.
Here is a comparison shot of un-roasted versus roasted beans.
I don't think it should be taking this long for the beans to get that dark. I suspect that the old popper I am using does not put out as much heat as it once did.