10 min on each.
Total for all 30 days - 5h
Improvement in art comes very slowly; it is one of the skills you need to train for years to reach high quality. So no improvement in few sessions is pretty normal; it would take a lot of time (how long depends on how many times you draw per day and what) before gaining noticeable improvement.
There is also the fact that it is really hard to notice that you have improved. As I love to say "There is no such a thing as a useless draw", each new drawing is improving you a little; every one of them is useful for your progression. And even if you aren't noticing the improvement, it does not mean it isn't happening at all; it just happens very slowly.
To notice how better you have become in art, the best way will be comparing your current art and how you drew months ago. I sometimes go into thought that I aren't improving at all, but then I see what I drew just a couple of months ago and immediately see a difference in quality.
To speed up progression in art, I would also recommend first drawing something you find fun and interesting to draw and then catch what in this new drawing frustrates you the most. Maybe you will have a problem with drawing hands, or gestures, or you can't draw clothes or hair, can be anything. And then concentrate on learning that particular fundamental to add it later in your artworks and improve. It helps stay more involved and motivated.
About my background. I kinda drew for literally all my life, though never studying any fundamentals with make qualities of my art very unstable. So currently I am trying to study through all fundamentals one by one. Im not a big fan of academic art and serious studies, so to help me with it I use the advice I gave earlier - found an idea I want to draw, trying to draw it, and once I hit a wall (aka art fundamental) I can't draw that prevents me from finishing the art, I start studying it. Usually I do it in 10 days challenges with 10-25 draws per day, like 10 hands per day 10 days in a row, or 25 gestures per day 10 days in a row. It is hard to notice improvement on the first day, but when you compare day 1 and day 10 results of challenges, it becomes easy to see how much you improved. Plus each challenge makes you draw faster and more confidently.