Twitter knows when you sleep

For example, waking/sleeping times are relatively constant throughout the year in Tokyo, but the other cities exhibit seasonal variations. We see that Japanese users’ activities are concentrated in the evening, whereas in the other cities there is more usage during the day. In Istanbul, nights get shorter during August; Sao Paulo shows a time interval during the afternoon when Tweet volume goes down, and also longer nights during the entire year compared to the other three cities.

Twitter Engineering: Studying rapidly evolving user interests. (via)

See also: When do they sleep?