Previously it has been shown that fusion chain reactions in the D–D system are feasible with supra-thermal deuterons in the MeV regime, with new generations of deuterons being produced by neutron knock-ons. Here we expand on this analysis via time-dependent simulations, in order to study the time-scale on which these chain reactions develop. We conclude that, at very high densities, it could be possible for strong development of the chain reactions in 5ps, putting the development of the chain reaction within the inertial confinement time.