The Federal Reserve’s long-awaited liftoff on its benchmark interest rate won’t happen until September, according to economists surveyed by Bloomberg News, as officials try to spur inflation and hiring after the economy stumbled in the first quarter. A hiring slowdown last month is adding to caution inside the Federal Open Market Committee, said Thomas Costerg at Standard Chartered Bank in New York. Seventy-three percent of 59 economists said the first rate increase since June 2006 will come in September, according to a Bloomberg survey conducted April 22-24.