surprisingly it can take as little as 30 minutes for a sperm to reach an egg in a woman's fallopian tube. however sperm can live up to 72 hours (3 days) inside a woman's body so fertilization could occur anywhere between 30 minutes and 3 days. this slideshow by webmd gives a great visual overview of the process of conception. i hope this answers your question!
following ejaculation how many days does it take sperm to reach the egg?