I doubt you'll get a precise, definitive answer for this.
There's no mention of injector latency in the Fiat injector specifications document, suggesting that it was considered low enough not to be mentioned.
Also, the exact measurement will vary depending on fuel pressure, fuel temperature, battery voltage, alternator output, injector wear and the exact driving electronics (ECU dependent) etc. Therefore the same injector will show different latency under various testing conditions.
Generally the opening latency is around 1 to 1.5ms, with closing latency under 1ms, so you can usually assume that the injector will be partially open for around 0.5 to 1ms longer than the pulse time.