Does Plan B one step really work if I take it during ovulation or after ovulation? Because wouldn't the egg have appeared already and have met sperm?

Works more than 1. Way. Plan b can prevent the ovary from releasing an egg, thickens cervical mucus which makes it harder for the sperm to reach the egg and thins the lining of the uterus to prevent implantation. You should use protection every single time you have vaginal intercourse if you are not ready to become a parent.