how long does morning after pill work?
1 When a woman ovulates, the egg is able to be fertilized for 12-24 hours (1 day). 2  When sperm enters the woman's body, it remains alive and able to fertilize an egg for 1-5 days. 3  It takes emergency contraception from 12-24 hours to be effective (1 day).  Emergency contraception remains effective for at least 10 days.