What is your definition of the "right" time to inject fuel? If you're only controlling fuel and leaving the stock ignition alone, then you can tailor the injection point to just about wherever in the cycle you want by changing the trigger position. However, like we have said, the actual injection point is not that important.
The first automotive EFI sytems were "batch fired", that is sets of multiple nozzles were fired simultaneously whether it was time for the intake cycle on a particular cylinder or not. The worst example (and I mean worst in the literal sense) of this is the "throttle body injection" units that appeared on some stuff out of Detroit in the eighties, but those are nothing more that electronic carburetors, and should be forgotten as quickly as possible. For the most part, batch firing was done with port located nozzles in sets of at least half the cylinders in the engine. The fuel delivered early simply piled up in the intake port. The most effective way this was done was to provide the same total number of shots as the number of cylinders in the batch, so that if it was a V8 with two batches, each batch would fire four times, each shot being a quarter of the amount needed. The one that happens during the actual intake stroke serves to "stir up" and re-atomize the earlier deliveries.
By 1990, this was nearly obsolete, and the best EFI systems available from GM in 2000 could control each firing of each injector and spark plug for each individual combustion event entirely independently based on current sensor output in real time up to the cut off at red line.
The point in this is that there is an ideal time to fire the nozzle, but there is also a considerable amount of leeway between ideal and entirely serviceable.