The maker explains at http://blog.blprnt.com/ -
GoodMorning! is a Twitter visualization tool that shows about 11,000 ‘good morning’ tweets over a 24 hour period, rendering a simple sample of Twitter activity around the globe. The tweets are colour-coded: green blocks are early tweets, orange ones are around 9am, and red tweets are later in the morning. Black blocks are ‘out of time’ tweets which said good morning (or a non-english equivalent) at a strange time in the day.
Much more info is at the post, with related images and explanation.