Use the --timeout flag to change the timeout.
--timeout
herbie shell --seed 2019088 (FPCore (t) :name "Kahan p13 Example 1" (/ (+ 1 (* (/ (* 2 t) (+ 1 t)) (/ (* 2 t) (+ 1 t)))) (+ 2 (* (/ (* 2 t) (+ 1 t)) (/ (* 2 t) (+ 1 t))))))