I received my first positive OPK on 6/24 and a negative on 6/25. I'm confused, did I ovulate on 6/24 or 6/25?

Has anyone else only received one positive OPK and the next day it was negative? I always thought women were supposed to receive two positives in a row to indicate ovulation? Help! I'm really hoping hubby and I will get a BFP this time!