Generation time has previously been the focus of comparative life history analyses. Here we examine three metrics: generation time Tc, reproductive dispersion S (the distribution of ages of reproduction), and damping time τ (time to converge to stable (st)age distribution). We use data on 633 species of animals and plants, and perform phylogenetically corrected analyses. First we find that S varies allometrically and isometrically with Tc. As a result, τ varies allometrically with either Tc or S but not both. Second, we find a trade-off between τ and S, so that τ does not vary isometrically with Tc. This trade-off is a novel demographic component to the relationship between τ, Tc and S that is otherwise partly determined by their similarity as biological times. Our results indicate that species at the slow end of the slow-fast continuum take longer to converge to stable distribution than species with fast life-histories.