Hey, just took a look at both images. First, I have to say for the first image, I honestly love how you use your lines. I can see the form/motion you are trying to convey with your line work. I would say try to practice 2 minute gestures, to really hone in on how you want your gesture to look. It's not too long and not too short a time, to really start warming up, for longer drawing sessions.
In your second image, I see that your 5 and 10 minute sketches, look more detailed/refined. However, it seems your shading keeps changing on various parts of the body. I would say try to stay consistent with whichever shade you choose, instead of switching back and forth. I personally love the 5 minute one, I can see the form and movement you want to convey, while the shading adds more emotion to it, in my opinion. Really well done, keep up the good work.
P.S. I've also just gotten back to drawing after years of not doing it. One day at a time, one page at a time, one sketch at a time. You got this :)
As of this moment, to become good enough where I can create my own characters, outfits, poses, facial expressions. Hopefully I'll become good enough where I can work for an animation studio, or be part of a team that can create a beautiful animated story like Avatar.