I have been taking a few road trips lately where I have been sitting in the back seat. This gives me plenty of time to practice quick sketching. Most of these sketches were done in five seconds or less. That five seconds is for the basic line drawing. I paint them later in my studio, remembering the colors and values, or just making something up. Please note that the second sketch took a little longer, about 10 minutes or so. This is a good way to keep your eye/hand coordination in excellent shape.