Tokyo stocks opened mixed Thursday as dip-buying following the Nikkei index’s recent fall was offset by concern that an interest rate hike in the United States could come soon. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 19.81 points, or 0.07 percent, from Wednesday to 26,991.52. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was up 2.57 points, or 0.14 percent, at 1,894.42. Decliners were led by precision instrument and information and communication issues, while marine transportation and mining issues led gainers. At 9 a.m., th…