  The width $\Delta T$ of the deconfinement transition region is shown to
influence strongly the flow structure in the (Landau-) hydrodynamical expansion
of a quark-gluon plasma. For a sharp first order transition ($\Delta T=0$) the
mixed phase is rather long-lived, with a lifetime that has a maximum when the
initial energy density is at the phase boundary between mixed and pure
quark-gluon matter. For increasing $\Delta T$, however, the lifetime decreases
rapidly. Hadronic matter, however, remains long-lived as a consequence of the
rapid change in the degrees of freedom in the transition region and the
corresponding ``softening'' of the equation of state.
