It could be the quickest return on an investment this year. An investor looks to have saved hundreds of thousands of dollars on Thursday by switching from one exchange-traded fund focused on junk bonds, to a cheaper ETF with a similar strategy. All told, the transactions took 21 seconds, and could reduce the trader’s investment bill by about $600,000. More than $350 million worth of shares in State Street Corp.’s SPDR Bloomberg Barclays High Yield Bond ETF, or JNK, hit the tape in two blocks at 12:46 p.m. in New York, data compiled by Bloomberg show. At the same time, more than $331 million of BlackRock Inc.’s ... (full story)