Is Fertile Period Affected If Period Is Postponed With Primolut-N?

I am supposed to get my period on the ninth of this month. I have been told to take Primolut N, from the fourth, to postpone my period, as it is my wedding time. According to my menstrual cycle my ovulation period is from the 20th so is is relatively safe to have sex and not get pregnant the first few days after the 9th. Will this still be valid now that my period has been postponed?