It's really quite simple: No morning-after pill works during ovulation, as they're designed to delay it. If ovulation is already happening, Plan B (or any other emergency contraceptive pill) will have failed before it's even begun.

Will the morning after pill work if I have already ovulated?

Morning-after pills won't work if your body has already started ovulating. This is why timing is so important, especially if you're using Plan B and other levonorgestrel morning-after pills. (ella works closer to the time of ovulation than levonorgestrel morning-after pills like Plan B.)

How does Plan B work if you have already ovulated?

It works by temporarily stopping the release of an egg from the ovary, preventing fertilization if ovulation has already occurred, or, if an egg has already been fertilized, preventing it from attaching to the wall of the uterus.