Based on the concept of the incubation time of plastic deformation, an integral yield criterion is introduced and time effects of irreversible deformation are considered. The efficiency of the approach is demonstrated using micro and nanocrystalline nickel as an example. The parameters of the phenomenological model are treated physically from the viewpoint of the behavior of the defect structure of the material, which is controlled by the dislocation sliding and grain-boundary slip mechanisms in a wide range of the rate of deformation.