Void swelling in structural materials used for nuclear reactors is characterized by an incubation period whose duration largely determines the utility of the material for core components. Significant evolution of the dislocation and void microstructures that control radiation-induced swelling can occur during this period. Thus, a theory of incubation must treat time-dependent void nucleation in combination with dislocation evolution, in which the sink strengths of voids and dislocations change in concert. We present theoretical results for void nucleation and growth, including the time-dependent, self-consistent coupling of point defect concentrations to the evolution of both void population and dislocation density. Simulations show that the incubation radiation dose is a strong function of the starting dislocation density and of the dislocation bias factors for vacancy and interstitial absorption. Irradiation dose rate and temperature also affect the duration of incubation. These features are in general agreement with experiments for high purity metals.