I believe 2 days, although I've heard that in EWCM they can live up to five days... but by then most of them will be pretty dead or useless.

It's worth noting that the Y sperm are very short-lived, only a day or so inside a woman, but they're "top quality" and really fast and excitable. The X sperm are not as souped up but can last longer - basically, sperm have finite resources and the Y sperm go through those resources faster than the X, although as time goes on the more resources are used to stay alive so there may not be enough left in there to be all active over the eggie.

HTH!