We have fabricated submicron injection-controUed NbN links with gain and measured their injection-triggered superconducting-to-normal transition to occur in 0.5-2.6 ns at 4 K, governed by condensate dynamics. The transient pulse shape displays a rising-edge kineticinductance spike and a strong dependence on the amplitude of the injected quasiparticle current similar to microbridges driven by supercritical currents. A modified dynamic effectivetemperature model is used to interpret the transient time and the pulse shape.