Use the --timeout flag to change the timeout.
--timeout
herbie shell --seed 2020153 (FPCore (lam k) :name "(- (log (* (pow lam k) (exp (- lam)))) (lgamma (+ k 1)))" :precision binary64 (- (log (* (pow lam k) (exp (neg lam)))) (lgamma (+ k 1.0))))