  We study the time scale for pressure equilibration in heavy ion collisions at
AGS energies within the three-fluid hydrodynamical model and a microscopic
cascade model (UrQMD). We find that kinetic equilibrium is reached in both
models after a time of 5 fm/c (center-of-mass time). Thus, observables which
are sensitive to the early stage of the reaction differ considerably from the
expectations within the instant thermalization scenario (one-fluid
hydrodynamical model).
