From Zadar to Medjugorje there is a travel distance of about 265 km, which equals a bus travel time of 4-5 hours, timetable for buses from Zadar to Medjugorje you can find below. Alternative to the direct buses you can travel from Zadar to Mostar or Zadar to Split, and then take a bus from there on to Medjugorje, that should give more travel options.
Travelling with bus from the Zadar airport to Medjugorje is not possible but you can arrange for a door to door transfer, you can see transfer prices for various vehicles here