Trough out the year it is possible to travel from Split to Herceg Novi in Montenegro, the 300 km long trip takes 6-8 hours with bus, depending on bus route and traffic at the day of the travel.
Alternative to travel with at direct route it is possible to take one of the frequent buses from Split to Dubrovnik and then to catch a bus from Dubrovnik to Herceg Novi or to take a transfer from Dubrovnik to Herceg Novi which gives more flexibility.