I don't know for sure, but I can't imagine that it was possible to dump the torpedo quickly
It's quite heavy and IIRC the crane was quite small and could not be used to throw a torpedo over board easily. Two minutes seems to me much too short.
Anyway, I guess modeling all the reloading stuff realistically is just impossible. Far too many unknown issues.
I think it would be already fine if you could not dive during reloading (at least during most of the time). This would already force players to play realistically, i.e., only reloading torpedoes if there was no danger (as it was done in real life). If you get caught, well, bad luck.
Does anyone know whether a boat was ever caught during reloading of external torpedoes in the war?
Cheers, LGN1