Here's one of the exercises I did, mostly in an hour. It's a 14x20" watercolor paper sheet from a block, gessoed and painted with thinned acrylics. I had the basic idea of a tall range of violet mountains, with hills and meadows in the foreground. The idea is to work as fast as possible, and develop all the paintings at the same time, and I did all the mountains first, then all the skies, then all the foregrounds, one color at a time. After I got the foregrounds roughed in, I let it dry completely, then came back and tweaked them individually till I felt like stopping.
Funny things happen when you're working quickly on so many things at once. For one thing, it's a lot easier to keep from getting emotionally attached to any one of them, so you're not so afraid to try something you've never done before. In fact, you have to get more inventive, to keep them from all looking alike. And with all that quick action, things happen that you didn't plan, and you start getting comfortable with that. You don't worry about every stroke. You don't worry that no one will like it, or that it's not going to win any ribbons. As long as you keep working quickly, you don't have time to worry about anything. That's how I want to be all the time—painting and not worrying about it.