calculate injection time

On diesel cars, how do you calculate the optimal Injection Time where you need to bring in more of it - in "injection time (us)" and "rail pressure (MPa / bar)"? I did learn it, of course, but would be very interested of your ways. As far as learned it, i would need to use Fuel Injected as a reference (eg. BMW 520d F))

I work on ECM Titanium (by Alientech)

Anybody?

Are you referring to optimising your start of injection time on a diesel?