Knowing how long a pose will be and knowing what I can accomplish within a particular time frame is really important for how I approach drawing with a live model.

For example, let's say it's a five minute pose, I think it's reasonable to say that I probably won't get into a fully rendered light and shadow drawing in that amount time, but what about a fifteen or twenty minute pose? Suddenly that question gets harder to answer. I've seen students in class do a lovely line drawing and then with two minutes left on the clock start to add lights and shadow. Ultimately the drawing looks unfinished by the end of the pose whereas two minutes earlier they had a perfectly fine, finished drawing. Ask yourself before you go to the next stage of developing the drawing if you'll have time to get down what you need to before the end of the pose. In the example above with two minutes left on the clock I might quickly 'shadow map' so I can finish the drawing at a later time, or get my tools ready for the next pose.

As you gain experience your intuition for what you can get done in a given time frame will get more refined. I'd suggest timing the pose yourself and not just relying on the tutor or the model to run the clock.

Try and be mindful of the time and what you'll be able to do with it.

I've more to say on this subject but that's for another time!