Over the years I've attended many life-drawing classes, but one of the biggest problems was the lack of long poses. Many artists wouldn't know what to do when a session resumed after the 20 minute break, so 20 minutes or shorter became almost standard lengths of time to draw a human being! Not always, but too much of the time this was the case. Consequently, these two small life paintings were done in a sculpture class, and over 5 afternoons with the same pose. There are now many Academies all over the world that embrace the study of the human figure over a sustained period of time. The quick sketch is a good thing to do but again, it's often mistakenly seen as capturing the essence of a figure and no more need be done to the drawing. But essence is the life of a drawing, not just the suggestion of a figure. If you wrote a story in short-hand it doesn't automatically mean you've captured the essence of anything. A great novelist captures the essences of the characters portrayed in the book because the author brings them to life. For me, the same applies to drawing and painting. Of course spending a long time on a pose doesn't mean you've caught the essence of the figure before you, because bad paintings can take just as long to do as excellent ones, but it's good to be able to draw or paint the figure over a long period of time as a challenge and to arrive at something more 'there'.
The paintings and drawings below were done over various periods of time. The first and second took 20 x 20 minute poses to paint. The third, fourth and fifth were done over 4 x 20 minutes of posing and the final drawings were 10 minutes. Various mediums and time periods bring different results of course, but it's good to practise them all