Does post pill work a day after ovulation?

If you've already ovulated, then there may not be anything that the emergency contraceptive pill can do, if sperm has managed to get through. Your best bet would be to have a Paragard IUD fitted by a doctor, which can act as emergency contraception, by stopping the pregnancy from implanting. It can also remain in place, as longer-term contraception.

You can certainly try an emergency contraceptive pill, but I wouldn't be relying on that, alone, under these circumstances.

Only the Ella pill (Ulipristal Acetate) has proven that it can work during the 24 hours around ovulation, itself, but even that is not guaranteed. Levonorgestrel, the ingredient in the other emergency contraceptive pills, is not proven to work during that time. It may help, but it is not proven.