Starting with your cylinders around arbitrary minor axes, you started off with a bit of a bump in the road, but ultimately did end up bringing it around. The main issue is that when you started out (and sporadically throughout the set), you were specifically drawing cylinders with side edges that did not converge - effectively placing that vanishing point at infinity. Unfortunately, that's not strictly something we can just assert for ourselves.

What we have control over instead is the orientation of the form itself, which in turn is what determines where that vanishing point goes. The vanishing point itself only goes to infinity (in the manner discussed back in Lesson 1) when the set of lines it governs (the side edges) are running perpendicular to the viewer's angle of sight - effectively not slanting towards or away from them through the depth of the scene.

Of course, this only happens in a very specific set of circumstances, all of which require the cylinder to be aligned in a rather specific fashion. Given that this challenge, like the box challenge, has us rotating forms freely in space, we can pretty much assume this will never happen, and that we should always be working with some convergence for those side edges. So, keep that in mind - if you end up with lines that are specifically running parallel to one another on the page, consider why that's happening, and whether it should be happening.

Aside from that, you're doing fairly well. You're executing your ellipses with confident and from the shoulder, achieving smooth, even shapes as a result, and your side edges are drawn to be fairly straight and consistent. You're checking for errors fastidiously as well, identifying fairly small mistakes, which will continue to help you refine your approach. And lastly, you appear to understand - at least on some level, whether instinctual or consciously - how the two "shifts" from one end to the other (the shift in scale where the far end is smaller overall than the end closer to the viewer and the shift in degree where the far end is wider) operate in tandem, both consistently conveying how much foreshortening is being applied. These have to work together - with a dramatic scale shift being matched with a dramatic degree shift, or a shallow scale shift with a shallow degree shift - as they both convey the same thing. If we were to have one be more dramatic and the other more minimal, then they would contradict one another and create confusion for the viewer. You may already grasp this - but I felt it was important to explain it anyway, in the case that it was more of an instinctual understanding.

Continuing onto your cylinders in boxes, 50 minutes per page is nothing to be worried about. That's a pretty normal amount of time for a single page of boxes from the box challenge, without the cylinders themselves. Regardless, it seems to have paid off, as your work here is quite solid. This exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

I have just one recommendation - when we identify the minor axis for our ellipses here, we are not doing it in the same way as the previous section of this challenge demanded. There we were merely pointing it out, but here our intention is to actually extend the minor axes back and compare them to the box's own implied vanishing point. If we only extend them slightly, we're not able to get that proper comparison, and so there's an area for mistakes/inconsistencies to hide without our detecting them.

So! Be sure to keep that in mind. I'll go ahead and mark this challenge as complete.