The time you see on tweets is the reader's time, not the time of the person posting the tweet. In other words, different time zones will see different times on tweets, depending on where they live..
I am in a time zone (CST), that is one hour behind Valdosta, Georgia (EST), where Kendrick Johnson was found dead at 10:30 am on January 11, 2013. So this tweet that was alleged to have been tweeted at 7:34, shows 9:34 am CST on my computer, which would make it 10:34 am EST, in Valdosta -- when and where, respectively, the tweet was Posted. I am not sure where 7:34 came from - but I have my suspicions :)
The next tweet mentioned: "At 8:36 am, a Lowndes High parent (off-campus) received a tweet which reiterates that a body was found."
Here is what I see, 10:36 CST, which would be 11:36 EST Valdosta time:
The next tweets mentioned: "As early as 9:51 am in the morning, there were tweets that local authorities from Thomasville's GBI office and the Lowndes County Sheriff's Office were already on the scene." I see 11:51 am CST, which would be 12:51 PM EST
Please note: The actual tweets have been removed from the Examiner article since I posted this the first time. Nevertheless, the above are the tweets and the times that coordinate with just the wording of the article.