Your surge is when you actually ovulate. Your fertile days are the 3-5 days leading to ovulation. This is because sperm can live instead after sex for up to 3-5 days, so if you have sex a few days before, they can be in there waiting on the egg. Only super strong sperm can generally live for 4-5 days, most only survive a max of 48-73 hours.
Ur fertile days are 5 before. Ovulation itself only really last 24 hours