From Zadar to Mostar there is a travel distance of about 300 km, which equals a bus travel time of 5-6 hours, timetable for buses from Zadar to Mostar you can find below. Alternative to the direct buses you can travel from Zadar to Split, and then take a bus from there on to Mostar, that should give you more travel options.
From the Zadar airport, there are no buses departures, but from the airport you have option to book a transfer for small or larger groups, here you can see transfer prices for various vehicles