  We show that the failure time $\tau_f$ in fiber bundle model, taken as a
prototype of heterogeneous materials, depends crucially on the strength of the
disorder $\delta$ and the stress release range $R$ in the system. For $R$
beyond a critical value $R_c$ the distribution of $\tau_f$ follows Weibull
form. In this region, the average $\tau_f$ shows the variation $\tau_f \sim
L^{\alpha}$ where $L$ is the system size. For $R<R_c$, $\tau_f\sim L/R$. We
find that the crossover length scale has the scaling form $R_c \sim
L^{1-\alpha}$. This scaling has been found to be valid for various disorder
distributions. For $\delta<\delta_c$, $\alpha$ is an increasing function of
$\delta$. For all $\delta \ge \delta_c$, $\alpha$=1/3.
