Use the --timeout flag to change the timeout.
--timeout
herbie shell --seed 2019088 +o rules:numerics (FPCore (x l t) :name "Toniolo and Linder, Equation (7)" (/ (* (sqrt 2) t) (sqrt (- (* (/ (+ x 1) (- x 1)) (+ (* l l) (* 2 (* t t)))) (* l l)))))