Doing a quick sketch of a person in real life is very different than drawing from a photograph, and it's a much more pleasurable experience. Seeing and sensing the spaces around the model and picking up the mood and likeness of the person is a fun and interesting "game". Poses in a life drawing session are usually as short as a minute or 2 and as long as an hour or 2.
I especially enjoy the challenge creating a sketch of a person entails. I concentrate on sensing every relationship both visual and kinesthetically, then recording those sensations as I draw. If you want to get better at drawing, there is no substitute for drawing a real-life model -- no photos or videos. Photos and videos are great reference for the experienced artist, but for the person wishing to use sketch time as a time to hone the craft of drawing, real life is the only thing to work with.
This graphite 6B pencil sketch on a drawing tablet was about a 10 minute sketch. I do a lot of sketches that don't work out, so even though the 10 minutes involved in this sketch may seem like a simple thing, when I factor in all of my less successful explorations and experiences, the time is a lot longer.