Will plan b one step work after/during ovulation?

Plan B: Is 95% effective when taken within 24 hours of unprotected intercourse. No contraceptive is 100% effective.

Yes: Yes, Plan B reduces the chance of pregnancy by a factor of 10 when taken within 72 hours of an unprotected encounter, even during or after ovulation. It does not work by inhibiting ovulation; it inhibits implantation which is a separate process that must occur before a pregnancy is established.