It takes sperm approximately 36 hours to fertilize the egg after the male ejaculates in the vagina. If you are asking "how long does it take for the sperm to fertilize the egg once it penetrates the egg wall?", it is instantaneous. That's what "fertilized" means. If you are asking "how long does it take the sperm to fertilize the egg once it enters the female body?", there is no exact answer. it could take from a few minutes to a few days. If you're seeing a fertility specialist they will give you a series of medications to cause you to hyperovulate. The specialist will give you a special ultrasound that will determine how many follicles are produced in you're ovaries. (follicles house the eggs until maturity then they release them) Once they determine that follicles have reached full growth, they will give you a shot of HCG. It will then take approx. 36 hours for the ovaries to release the mature eggs. However the egg can only survive up to 24 hours without fertilization via sperm. Sperm can survive up to 5 days in body to search for the unfertilized egg.