Having only written two hubs, perhaps my answer may not appear to be the best representation of hubbers.
However, I find it takes me several hours to write a hub, although I have been working on one now for a couple weeks (off and on). The research or gathering of material takes about an hour or two previous, and then it takes me about a 2 hours to write, then after I write, I go back and proofread everything a few times, which takes about an hour. I then finish the layout and publish! The hubs I have published, I spent a good chunk of my day writing... so, it is difficult to say. I think the amount of time put into a hub results in the quality and density of the subject on which it is published. You can tell when a person spends time on their hubs. They are generally more informative and readable. So! I have no idea how much time others spend on their hubs. But I like the ones that have been well thought out.