any ways u have not told about period date so I can't tell u exactly when to start primolute n to prepone or postpone the date.in general if u want to postpone then u have to start it 7 days prior to menses date till the date u want to postpone ..twice a day.  for prepone u have to start from day 20 of your menses twice a day for 5 days.so it may come within 5 to 7 days but not fixed.so postpone menses always better.