Why don't you READ THIS and try to comprehend what the words say....
Fertilization is the process by which two gametes (reproductive cells having a single, haploid set of chromosomes) fuse to become a zygote, which develops into a new organism. Fertilization includes the union of the cytoplasm of the gametes (called plasmogamy) followed by the union of the nuclei of the two gametes (called karyogamy).
It IS A PROCESS....
Conception (from medical definition)
is an imprecise term denoting the formation of a viable zygote.
The pertinent words being "imprecise", and "viable"....
Viable means capable of living, developing and growing, etc.
I think my logic is reasonable and sound...
A sperm penetrates an egg, starting a process (fertilization)
A viable zygote is formed (capable of living, developing, etc.)
At the moment in time that the zygote becomes viable, a human being is created and grows, develops, matures and dies....