A theoretical study is performed on the ultrafast transient transport properties of photoexcited carriers in zincblende GaN subjected to electric fields up to 120 kV/cm. Depending on the photoexcitation degree, the subpicosecond electron and heavy-hole drift velocity evolution towards the steady state presents maxima and minima, e.g. a structured transient. Since nonequilibrium phonon effects are not included, the structured ultrafast carrier drift velocity is explained through the crossover of the evolution curves for the transport and momentum relaxation times, whose definition is based on the nonequilibrium variables used to describe the system.