Ovulation takes about 24 hours. The egg may live up to 2 days in the fallopian tubes so you can still get pregnant within this time frame. You can have sex a couple days before you ovulate and get pregnant as the sperm can live several days inside the woman's body. For a woman who has a 28 day cycle she should ovulate on the 14 day after the first day of bleeding. This is just a general rule as you may or may not ovulate on the same day of your cycle from month to month. Also if your periods are longer/shorter/inconsistent your ovulation day would be different.