You'll never guess which was the 10 min one

Nice job on your (I think) 30 minute class, Idrinkmonet. Yet, I have my critique of this. You're just a little bit too fixated on the details. Why don't you do 5 min and 30 seconds of 30 second gesture drawings, pretty please??? The truth is because, you'll be even more than focused on the energy and vitality of your portraits facial. I anticipate that it'll help out too much.

Polyvios Animations

Great expressions. And on the more complete faces, you are hitting ther proportion nicely. I did notice that you are drawing your gestural guidlines and then kind of ignoring them when you are starting in on the details. Those gestures are essentially the skull. So it looks like you're drawining the skull and then drawing a different face on top. You get credit for draing a successful face, but the skull isn't part of the equation.

For some future exercises, I suggest doing a bunch of 30sec or 1 min poses, like 10-20 (you decide what enough is). And only drawing the head gestures that you are already doing, with the "t" lines that you also do to establish directions. Then when the session is done, go back and draw a full skull over those lines in exact proportions to the gestures. Then take some tracing paper or erase the skulls just enough to see, and put a face with each facial feature where they belong. They dont have to look like the original model, they just need to look like an average human with their features properly placed. It would be helpful if you have some kind of 3d model of a skull to use as reference, and a reference of basic anatomy of the face so you can see how exactly each feature, like the nose and eyeballs fit on or in the skull.