The timing of the Federal Reserve’s interest rate hike, which would be its first in nearly a decade, is unclear and for now policymakers must watch that the U.S. economy’s surprising recent weakness does not signal a more substantial slowdown, a top Fed official said on Monday. New York Fed President William Dudley’s comments were the latest sign that a string of disappointing economic data, including a sharp drop in jobs growth last month, is derailing a Fed plan to tighten monetary policy around mid-year after more than six years of rock-bottom rates.