I'm not sure you're right about there being no 'precise moment' at which conception occurs:
When that single 'lucky' spermatozoon breaches the ovum's membrane and the ovum immediately renders its membrane impervious to penetration by additional spermatazoa, conception has occurred. The fact that we almost never see that very rapid event occurring doesn't change the fact that it does occur.
The fact that we almost never see that very rapid event occurring doesn't change the fact that it does occur. I'm not sure I understand you here. If you are saying that the process of conception does occur, then of course I agree that is true, and it is as much a matter of observation as the fact that there is no precise time point dividing gametes from zygote.