Big retailers such as Target Corp. and Wal-Mart Stores Inc. aren't the only stores opening early for "Black Friday" this year. The Mall of America says more than 180 stores in the Bloomington megamall will open at midnight on Black Friday. That's about 35 percent of the approximately 520 stores that are at the mall. And the mall expects about 200,000 Black Friday shoppers this year. The midnight opening time is three hours later than when Target (NYSE: TGT) stores will open on Thanksgiving, and…