Painting at sunrise is one of my favorite things to do. The light changes so quickly that you have no choice but to simplify. I prepare for painting the night before. My brushes are clean, palette is clean and fresh paint is squeezed out. I hate rooting through my back pack trying to find a specific tube in the dark or low light and it eats up valuable painting time. Sunrise and sunset seem to be the easiest to paint. I find mid-day the most difficult. The color of the light, lack of good shadows, everything seems flattened out...much harder decision making process.
Best of all, before most people have even thought about their first sip of coffee, I've completed a painting!