June 16 (Reuters) - The S&P 500 and the Nasdaq opened just below record highs on Wednesday, with investors on edge before potential hints from the Federal Reserve on when it would taper its massive monetary stimulus. The S&P 500 opened higher by 2.28 points, or 0.05%, at 4,248.87, while the Nasdaq Composite gained 12.69 points, or 0.09%, to 14,085.55 at the opening bell. The Dow Jones Industrial Average rose 9.15 points, or 0.03%, at the open to 34,308.48. (Reporting by Sagarika Jaisinghani in Bengaluru; Editing by Maju Samuel) Our Standards: The Thomson Reuters Trust Principles.