a critical point or pnr (point of no return) is the last point you have fuel to divert or return to the airfield being considered
Waren I think you may be confusing the terms.
Critical Point or Equi-time point is where the TIME to two destinations is equal. It does not take into consideration fuel. It is all about TIME.
PNR is about how far one can fly, often from the departure airport but also can be an off track PNR, and still return to a nominated airport. PNR is all about FUEL which obviously translates to time in the air.
Because in aviation we are not happy unless we keep changing the name of things to suit the latest whim (AFIZ, MBZ, MTAF, non towered...) the acronym LPSD latest point of safe diversion is also used. I stuck with CP/ETP and PNR to KISS.
Am I missing something, happy to be wrong.