minutes of ejaculation cinq jours just minutes 50 percent of all fertilized eggs about half fail to implant 12-24 hours Conception: How It Works University of California San Francisco Medical Center bit more intricate than that five days About half five days 5 or 6 days 30 hours up to 5 days Conception — How It Works (UCSF Medical Center) fertilized egg (embryo) 50 percent of all fertilized eggs 5 days "Conception: How It Works" that can go hideously wrong About half of all fertilized eggs fail to attach, which some estimate "Conception: How It Works" five days fertilization bit more intricate than that