If taken before ovulation, plan b affect ovulation date & pushes it further or skip it?

Plan B delays it. “Plan B temporary stops the release of an egg from an ovary. Prevents Fertilization. Prevents a fertilized egg from attaching to the uterus.” REF: http://planb.ca/how-it-works.html.
Pushes further. Plan B will effectively delay your period by delay your ovulation by about 1 week. The medication stops the signal for ovulation, which could come about after the pill is used.