Depending on how detailed a mini is, anywhere from 15 minutes to an hour per mini for me to paint it, aroundabout 3 hours for a single mini including priming, painting, and sealing (each takes about an hour, mostly down time waiting for the previous coat of primer/sealer to dry before applying the next). And I've gotten pro-level results with that (friends and brother - all who are very detail oriented and very critical - all say that I could sell my work for about $30 a pop for a 32mm miniature, and I have sold a couple at that price level). You just need to find techniques that work for you - I do a lot of drybrushing, which is fast, and tends to give me really good results (I need to get some micropens so that I can start doing eyes, though...).
On the other hand, I've heard of people that spend 40+ hours on a single miniature, and can sell their work for over a thousand dollars per mini - but that is way over and above what I want to do with it, and just seems like a waste of time for the most part. But that's just me.