The dynamics of the image quality reconstructed from holographic photopolymer is experimentally investigated. In experiments, the intensity and quality of reconstructed images are monitored during dark enhancement and uniform post-exposure. The quality of reconstructed images is quantitatively evaluated based on the loss of signal-to-noise ratio. The experimental results show that the intensity and quality of reconstructed images suffers from non-monotonic changes during dark enhancement and uniform post-exposure, that is, increases at first, but decreases later from the highest value. These experimental results can be explained by the formation and development of noise gratings. The tolerance of image quality on uniform post-exposure and dark enhancement is evaluated based on the characteristic time, at which the signal-to-noise ratio of reconstructed images decreases a half of the original value. The experimental data show that during the characteristic time, both of quality and intensity of reconstructed images are acceptable. In multiplexed holographic storage, the dynamics of image quality should be considered in order to ensure uniform diffraction efficiency and good quality to all holograms.