We study the effects of independent, identically distributed random perturbations of amplitude " > 0 on the asymptotic dynamics of one-parameter families ¹f a W S 1 ! S 1 ; a 2 OE0; 1º of smooth multimodal maps which are "predominantly expanding", i.e., jf 0 a j 1 away from small neighborhoods of the critical set ¹f 0 a D 0º. We obtain, for any " > 0, a checkable, finite-time criterion on the parameter a for random perturbations of the map f a to exhibit (i) a unique stationary measure and (ii) a positive Lyapunov exponent comparable to R S 1 log jf 0 a j dx. This stands in contrast with the situation for the deterministic dynamics of f a , the chaotic regimes of which are determined by typically uncheckable, infinite-time conditions. Moreover, our finite-time criterion depends on only k log." 1 / iterates of the deterministic dynamics of f a , which grows quite slowly as " ! 0.