I should also have mentioned that there's a school of thought in film-making that you leave your camera at a fixed WB, normally something like 5500K, and so during the day will look slightly blue and evenings will look slightly warm. The rationale is that this is how we experience reality, and also if you're shooting in a more documentary style, then having the time of day reflected in the images is also a visual queue that adds authenticity, because the WB of every shot is contextually relevant.