Novel techniques in the field of wavefront shaping have enabled light to be focused deep inside or through scattering media such as biological tissue. However, most of these demonstrations have been limited to thin, static samples since these techniques are very sensitive to changes in the arrangement of the scatterers within. As the samples of interest get thicker, the influence of the dynamic nature of the sample becomes even more pronounced and the window of time in which the wavefront solutions remain valid shrinks further. In this paper, we examine the time scales upon which this decorrelation happens in acute rat brain slices via multispeckle diffusing wave spectroscopy and investigate the relationship between this decorrelation time and the thickness of the sample using diffusing wave spectroscopy theory and Monte Carlo photon transport simulation.