From Zurich to Split there are buses driving year around, the buses departure from the bus and carparkplatz at sihlquai. Check the ICONs in the timetable below to see operational days and period of the buses. Travel time for the 1170 km long bus route from Zurich to Split is about 18 hours.
If you are going on Holiday and plan to return to Zurich with bus, you should buy a return ticket as this is cheaper then two single tickets. Return timetable Split to Zurichyou can see here.