The quasi-equilibrium state in vapor and the establishment of this state during free molecular and diffusion absorption of vapor by the growing supercritical droplets were studied. The time of the establishment of the quasi-equilibrium state in vapor, the duration of the stage corresponding to effective nucleation of the supercritical droplets, and the characteristic time of the variation of supercritical droplet radius at this stage were estimated under supercritical droplet nucleation conditions on the macroscopic condensation nuclei and the gradual creation of the melastable state in vapor. The hierarchy of the kinetic time scales was revealed. This hierarchy is needed to describe the stage corresponding to effective supercritical droplet nucleation and allows us to understand the complex multistage mechanism of this stage. The possibility of neglecting the curvature of the surface of supercritical droplets at the stage corresponding to their effective nucleation was substantiated. The smallness of the supercritical droplet radius at this stage when compared to the sphere radius of vapor absorption by the droplet was proved.