  We analyze the effects of different forms of the sound-velocity function
cs(T) on the hydrodynamic evolution of matter formed in the central region of
relativistic heavy-ion collisions. At high temperatures (above the critical
temperature Tc) the sound velocity is calculated from the recent lattice
simulations of QCD, while in the low temperature region it is obtained from the
hadron gas model. In the intermediate region we use different interpolations
characterized by the values of the sound velocity at the local maximum (at T =
0.4 Tc) and local minimum (at T = Tc). In all considered cases the temperature
dependent sound velocity functions yield the entropy density, which is
consistent with the lattice QCD simulations at high temperature. Our
calculations show that the presence of a distinct minimum of the sound velocity
leads to a very long (about 20 fm/c) evolution time of the system, which is not
compatible with the recent estimates based on the HBT interferometry. Hence, we
conclude that the hydrodynamic description is favored in the case where the
cross-over phase transition renders the smooth sound velocity function with a
possible shallow minimum at Tc.
