To answer your question, the cylinders are recommended to be completed after Lesson 5, before Lesson 6, since that's when students generally have had more opportunity to get comfortable with ellipses (and they tend to be less panic-stricken by the line extension stuff for the cylinders in boxes). Prior to that, you're not required to jump into the cylinder challenge at all, so even if I did assign revisions, you would always have the option to continue onto Lesson 4. So, while I haven't gone through your work yet, the answer to your question is yes - if I were to assign revisions, you'd still be free to continue onto Lesson 4.

Anyway! Jumping right in with your cylinders around arbitrary minor axes, despite starting on the challenge earlier than recommended, your work here is pretty solid. Your ellipses are confidently drawn so as to maintain even shapes, your side edges are smoothly executed resulting in straight lines, and you've been quite fastidious in checking the alignment of your ellipses, catching not only cases that are more obviously off, but those subtler discrepancies that can easily be missed as well.

One minor point to keep in mind - and you're applying this a fair bit already, but it's a little inconsistent and may only be something you grasp on a more subconscious level at this point - is that when it comes to how much we shift the degree of our ellipses (making them wider the further away from the viewer they get), this should operate alongside the shift in scale (where the ellipse gets smaller in its overall scale, the further back we slide along the length of the cylinder). Both "shifts" represent the same thing - they tell us how much foreshortening is being applied to the form, or in other words, how much of the form's length can be directly measured on the page, versus how much exists in the "unseen" dimension of depth.

Since both of these shifts represent the same thing, they work in tandem - the more dramatically the far end gets smaller, the wider it should also become.

Continuing onto your cylinders in boxes, your work here has largely been done pretty well, aside from a few one-off instances of inconsistency in applying certain line extensions. 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.

As mentioned previously, I did notice some places where some line extensions were missing - primarily on this page, where 196 and 197 are missing the blue line contact point line extensions. Initially I thought this might be a pattern of behaviour, but I'm not able to find other similar clusters of cases, suggesting that it may have instead been a one-off issue. Either way, the rest of your work demonstrates a good grasp of how to apply this methodology, so as to develop your understanding of those proportions as you continue to apply it in your warmups.

All in all, solid work. I'll go ahead and mark this challenge as complete.