The evolution is superb! Your commitment and perception are very good.
I really loved the 2min and 5min sketches, specially for the different sizes (and, thus, the use good use of the page) and the clean lines/contours.
I'd say to use the same principle of the clean lines when drawing the 30s or 60s sketches - in other words, be bold and make the curved or straight lines in a single movement of the hand. Try warming up before training sketches, to loosen up and be less worried about the quality. Mistakes will happen, it's normal.
The feet and hands from the 5min sketches are also very good!
Furthermore, start practing foreshortening and other perspectives. I know you will like this challenge :)
Keep going, friend! :3