How to stretch 1ns pulse into a 5ns pulse?
Sounds like you'll need a really fast comparator and a pulse stretcher circuit. For stretching the pulse (which is your question here) once you get it into logic level voltages, I think you could use a SN74AUC74 and feed the output back to the /CLR input through a delay. 

It's not safely capable of handling your high voltage 3.3V supply but that could be dealt with in one or more ways. With a 1.8-2.7V supply it is guaranteed to respond to a 500ps pulse.