Positive OPK not matching BBT?

Briana

Last week I was taking Clearblue Advanced OPK’s. I received a peak result on CD15 which historically speaking is a little early for my cycle but flow changed my O date to the next day. My BBT was not showing ovulation. Fertility friend just picked up a possible O date on CD18 which is when I normally ovulate. Is it possible to have an LH surge for 2 or 3 days? I’ve never had this happen and I’m a little confused. Anyone have experience with this?