Instantaneous. : Ovulation happens as an instantaneous event usually on day 14 of a 28 day cycle. The signs of ovulation start a day or two earlier and continue after ovulation has occurred. When an egg is released it retains its maximum fertilizing potential for about 24 hours after which it dies....Read more.he signs of ovulation start a day or two earlier and continue after ovulation has occurred. When an egg is released it retains its maximum fertilizing potential for about 24 hours after which it dies.