Use the --timeout flag to change the timeout.
--timeout
herbie shell --seed 2019100 +o rules:numerics (FPCore (t l k) :name "Toniolo and Linder, Equation (10-)" (/ 2 (* (* (* (/ (pow t 3) (* l l)) (sin k)) (tan k)) (- (+ 1 (pow (/ k t) 2)) 1))))