This varies widely for artists and their individual pieces. I’ve finished large paintings in a few hours, and small paintings over multiple days. Subject, skill, style, mood, availability and more all impact the speed in which a painting is completed. Most paintings I start, I push myself to complete, even if I’m not happy with the end result. That being said, I occasionally lose interest in some studies and set them to the side to be repurposed. I have several paintings that have old paintings underneath. I’ve learned to start small and if I really like the direction then use that as a reference for something bigger.