You have some excellent work here.
Strong understanding of form and porportion, your lines show confidence, and your foreshortening is on point.
Your drawings are dynamic and show a lot of movement and fluidity. I also love the shading on the first one!
For improvements it would be useful if you tried to think about your sketches in 3d space when it comes to the ones with less time allowed to them, for example using cylinders and cuboids or even just framework around the fingers (like rings) to help you think about it more that way when it comes to more detailed drawings.
Keep up the great work!