Fri, May 24, 2013, 1:19 PM EDT - U.S. Markets close in 2 hrs 41 mins
I can't find any news for CHLN, and it looks like it might've opened trading late(?). Maybe the market maker needed the extra time to line up sellers to meet one large buy order? That's a total guess, but it's the only one I've got right now.
You might be right. Major trading began around 10:15 and continued with about 300,000 shares until a little before 11:00.