You are amazing! I like your paintings here and this exercise that you share with us. I like the velocity and passion at which you are working, this is motivating and strong. This is enough to shake out any cob webs accumulated in my studio. I believe this is more important to the artist's soul and keeping it alive, if the 20 minute painting works out, then bonus. In these paintings you conquered subtle, getting values real well, limited palette is great, and developed a greater sense of realism. In 20 minutes , it may be wise to work with few values such as 3, 4. Your composition is not horrible, it just wasn't considered carefully enough beforehand on those tries. Just as you have to have your palette already to go, preparation of composition ready to go as well, this will help you to slow down and relax and boost your confidence. I disagree with no way of finishing a painting in 20 minutes, take @ Kaustav's recent Teddy Bear painting as just one example, but it doesn't always and rarely happens, but what an incredible moment it was. I believe this is what there is to live for in these kinds of exercises, that element of surprise, when and if, one works out. The ability to purchase a roll of canvas at a deal is great (just check it real well before purchase for quality control ) and use it as you need as you go works real well. Good work, keep painting!
I've brightened the highlights on the top petal and just a little more work on the left petal for now. The greatest challenge here was to avoid exaggerating these highlights. I feel confident enough to say I won't have to return to those later for any further adjustments. I am enjoying doing this piece.
I like how you used the term "sculpting" from the dark background, in your intro above. I am also a sculptor and this has occurred to me through oil painting process as well, that I was sculpting to 3D from my background but with oil painting technique. I was struck with inspiration by that insight and the seemingly parallel similarity while painting my own portrait recently. Glad you are having fun and enjoying it!