1. It helps completely to get occasional feedback, especially from people who are versed in it. Getting constructive criticism is a must. It's what helps pinpoint where your issues are and what you need to focus more on.
2. When it comes to the length of the sessions, it depends on your goal with having timed sessions. If you want to have more detail in your drawings, either do longer sessions or just don't time it at all. But regardless the length of the sessions, do as many sessions as you can. Practice, practice, practice and you'll get there.
The art classes at my college was a joke. I learned far much more from online tutorials than I ever did at my community college. I couldn't and still can't afford an actual art school college, and though I would love to do so, it doesn't really matter to me. I find I prefer to learn at my own pace, then again I have a mental disorder that makes going to school or work next to impossible... Anyhow, learn what you can within your current means and don't let not being in an art school deter you from making your art. If you really want to be an artist, then just draw and soak up whatever you can. Find your inspiration and soar.
Rakta pretty much summed it up, but something I want to add to that is you definitely show potential. If you really want to dive deep into art through drawings don't only do the ones on this site. Gesture drawing really is a good way to get started in your artistic endeavors, but don't only limit yourself to that, and keep at it. As you get better and better, you can get more detail in your 10 minute drawings. So keep hold of this one to look back on to see how your progress has been. I always find it interesting when I look back on my first drawings (I started with anime/manga style, I'm here for more realism and better fluidity) and then look at where I am now. It helps me with my confidence to see how much I have improved. I hope the same for you.
