Neglect is a conscious decision. Being unaware of something is not neglect.
If God had intended that only during optimum time would intercourse and fertilization occur he would have made us like the animals wherein sex is stimulated by the female going into heat. He did not do that hence sex is MORE than a reproductive scheme.
And a zygote is not life until it is implanted in the womb to be nurtured. Besides we do not know that any particular zygote will successfully implant even if the egg and sperm are perfect. Your attitude borders on fanaticism.
"If God had intended that only"
Wow. You KNOW God's mind. Pretty impressive. Can't argue with that.
Me, I have rely on the Bible, the Holy Spirit, teaching of Godly men and women through the years, and my brain.
But since, you KNOW God's mind and intention. You go on your way.