You caption your example of an injector current wave as:
"It can be clearly seen from the example waveform that the waveform is clearly 'split' into two easily defied areas. The first part of the waveform is responsible for the electromagnetic force lifting the pintle, in this example the time taken is approximately 0.6 ms. At this point the current can be seen to fall before rising again as the pintle is held open. With this in mind it can be seen that the amount of time that the injector is held open is not necessarily the same as the time measured. It is not however possible to calculate the time taken for the injectors spring to fully close the injector and cut off the fuel flow." https://www.picoauto.com/automotivetopic ... rrent.html
I don't see the .6ms you cite that the pintle stops opening at. It appears to be more like 1ms on your example. Also you say there isn't a way to check the closing latency, but it is in fact easily done and is just as important as the opening latency as it cancels some of the opening deficit and is needed to calculate the total latency. Here is how it's done. Find a Bosch detonation sensor (bolt hole in center type), either bolt a rod threw the center hole that can be used like a mechanics stethoscope or attach the det. sensor acoustically to the fuel rail. Using an inductive current probe on channel 1 and triggering on this channel, connect the detonation sensor output to channel 2. Channel 1 looks like your example scan and channel 2 will have a ringing wave on injector opening with the first up cycle closely aligned to the "knee" in the current, confirming the pintle has hit the full open stop. Use this to confirm that you are in fact seeing the pintle noise and not something else on the rail. Now the closing side will also have a bell ringing pattern, but the first down cycle of the ringing is the pintle fully closed point. This is always less then the opening latency for 2 reasons, one, fuel pressure helps close the pintle and two, a collapsing field inducts and magnetically aids the closing force (a diode in the control unit is usually in the circuit to control this).