The fastest swimmers may find the egg in as little as 45 minutes, while the slowest can take up to 12 hours. If they don't find an egg in the fallopian tubes at the time of intercourse, the sperm can wait there in a resting stage for up to 72 hours. Only a few dozen sperm ever make it to the egg. The rest get trapped, lost — perhaps heading up the wrong fallopian tube — or die along the way.