Sperm can last up to 72 hours. They say, in theory, that the highest chances of fertilization are the 12 hours before ouvulation and continuing 36 hours thereafter.
That said there are many factors tat can kill sperm right out of the gate (ph balance is off, not enough progesterone in lining, etc.). A pregnancy test wont show a postive unitl your body begins producing hcg (the hormone produced when you are pregnant--that's what the test's are testing for). Nornally that is, at a minimum, 7-9 days after ouvulation, I think.