Recently, when working with clients for a portrait session, I've been advising against my longest portrait session option, which comes in at 2.5 - 3 hours of photography. Some people actually do want this much time, and do need it, but for the most part I have found that my clients are more engaged and excited at the beginning of the session.
As an example of what can be done in a quick session, I have a selection of shots from my session with Erin. Erin wanted a new LinkedIn profile picture, as well as some more portrait-y type photos for herself. Also, because she's good like that, she had a few printed up and sent to mom for Mother's day. My mom is still waiting on the portraits she requested of me back in 2007. Oops.
We met around 6pm, wrapped up just before 7pm, and never strayed more than 2 blocks from my office. In that short window of time, we were able to get some fun photos, some LinkedIn options, and never had to break a sweat. In a new first for me, Erin also got a "hey there!" from a G train conductor in the form of a horn blow and a smile as the train passed.