The phase transformation of water into ice VI or ice VII under extremely high-pressure rates is studied. The model based on the incubation time approach is developed to predict critical conditions of water crystallization in dynamics and to plot a shifted diagram corresponding to experimental observations. Theoretical prediction appears in a good agreement with the experimental data. It was shown that the incubation time value of the phase transformation significantly depends on not only resulting temperature of dynamically compressed water while crystallization onset but also on the initial one at the unloaded state