Hi, I'm so excited to get the chance to improve my feedback skills haha.
Let me start of by saying that most artists have felt as if theyre loosing skills while practicing. Thats because youre inevitably going to hit a point where youre either leaving your comfort zone or growing more impatient and frustrated, which often translates through art. What often helps me is taking a step back and taking a day off to recharge (dont punish yourself with something you love).
I can clearly see that you've got an eye for proportions and the line of action which is a very hard thing to get for many people. You're doing great so far! This is what I would work on if I was you:
1) Quick studies (speed dating the human body haha). The better you get at something, the less frustrating things are overall, which is why I would recommend 5x 1 minute and 2x 2 minute figure drawings. Theyre great for loosing up and gaining quick experience without getting lost in the hard and annoying parts too much.
2) "draw what you see, not what your brain thinks it sees" I noticed that you use circles as guidelines for joints and then build/imagine the volume around that. This technique is very hard on the brain. Maybe you could try to look at specific body parts to get an understanding of how theyre connected, their volume, muscles and quirks. Studying anatomy can be really fun, but if you dont have the time you could also start by just looking at the figure drawing refernce for 30 seconds before you start drawing. Just take in what you see and try relying more on your eyes (opposed to your brain).
A lot lot of professional artist demonstate really loose and beautiful figure drawings. GrizandNorm and Ben Lo are some I found on Pinterest and really adore.
I hope I could help :)
I sometimes find myself with leftover time as well.
What works best for me is spending a few seconds in the beginning with a lighter under-drawing and depending on how much time I have left I'll go into detail in specific areas. Your figure as a whole shows that you've got a good concept of proportions, but next time you could look at some body parts like the knees (their shadows and volumes).
Maybe you could try doing a longer figure study on your own to get a better feeling for how much time you have left and to learn not to speed up things too much towards the end, especially if you have time left.
Hope that helps :)