If you're trying to conceive, it can live up to 3 days. If you're trying to avoid conception, it can live up to a week...
Obviously, the sperm cells aren't aware of your intentions, but if you really want to conceive, your best chance is if ovulation is within 72 hours - preferably less. If you really don't want to conceive, abstinence or birth control are highly recommended.
Good luck!
Rachel