Is it the moment the sperm fertilizes the egg or the moment the embryo implants on the uterine wall?
I believe that conception takes place (a new human life begins) at the moment a sperm fertilizes an egg; but that a woman is not technically pregnant until the egg is successfully implanted on the uterine wall.
But unless I miss my guess, your real question is whether human intervention to prevent a fertilized egg from going on its probable nine month trajectory from embryo to full-term delivery is, or is not, okay with God, under any given circumstances.
I believe it is not okay with God; but I don’t believe God condemns people for doing what He doesn’t want them to do (that is, for sinning):
John 3:17 For God did not send his Son into the world to condemn the world, but to save the world through him.
If you do a search for “conception” or “When does conception take place?” you will find that the general consensus is that “conception” is tantamount to “insemination” that is, the point at which the sperm unites with the egg.
“Implantation” is a different process that is considered to be “a stage of pregnancy” occurring 7 to 12 days after ovulation.