Here are a few more from recent weeks:
Not sure how long this pose was for, but I can assure you that the model didn't have a 5 o'clock shadow (such are the perils of using charcoal!)
This one was a 25-minute pose, pencil.
This was, I think, another 20/25 minute pose. Here, the tutor gave us each a small piece of card, about an inch and a half square, along with a piece of charcoal. We had to load the edge of the card with charcoal, and use this as a drawing implement. I really like the result.