Check out this cool video. Click the link to a YouTube video showing the whole first day of the event (Avenida de Colores in Sarasota, Florida, 2009), taken from a second story window overlooking the street. I'm in the upper left hand corner of the video.
It gives an interesting view of how long it takes to produce one of these works. And this is just Saturday, from about 9am to 9pm. We then worked most of the day, til 3pm on Sunday.