We consider interacting many particle systems with quenched disorder having strong Griffiths singularities, which are characterized by the dynamical exponent, z, such as random quantum systems and exclusion processes. In several d = 1 and d = 2 dimensional problems we have calculated the inverse time-scales, τ −1 , in finite samples of linear size, L, either exactly or numerically. In all cases, having a discrete symmetry, the distribution function, P (τ −1 , L), is found to depend on the variable, u = τ −1 L z/d , and to be universal given by the limit distribution of extremes of independent and identically distributed random numbers. This finding is explained in the framework of a strong disorder renormalization group approach when, after fast degrees of freedom are decimated out the system is transformed into a set of non-interacting localized excitations. The Fréchet distribution of P (τ −1 , L) is expected to hold for all random systems having a strong disorder fixed point, in which the Griffiths singularities are dominated by disorder fluctuations.