It states in the article researchers have found which times people are the happiest, and which times people are more likely to be sad:
"Mislove and Lehamann found that people are happiest on Sunday mornings and saddest on Thursday evenings. They also found the following mood pattern each day:
6:00-7:00 am: Happy Tweets
12:00-4:00 pm: Sad Tweets
Evening: Happy Tweets "