From Zagreb to Murter, there is a travel distance of about 340 km, following the Croatian highway. From Karlovac, it is possible to go via tool free local road, passing Plitvice lakes, this trip has app. the same distance, but is more time consuming.
Direct buses between Zagreb and Murter are limited to the summer season, each day there is about a handful of buses between the cities. Driving time with bus is about 5-6 hours. Most of the buses from Zagreb also stop in Jezera, Tisno and Betina.
Here you can see current timetable: