Spend the first night in Zagreb, then slow down with two nights each in Zadar, Split, Hvar Town and Dubrovnik. The contrast is the attraction: leafy city squares give way to Roman ruins, a palace still woven into everyday streets, and an island harbour where you can linger after the day-trip boats leave.
This is an active holiday with four hotel moves. Arrival and departure count within the ten days, so choose flights into Zagreb and home from Dubrovnik if the fares work. The island section suits late May, June or September, when sightseeing is usually more comfortable than in high summer. Check the seasonal Hvar–Dubrovnik connection before committing to dates.
Plitvice is optional. Drivers can make day two a lake visit on the way to Zadar; bus travellers have an easier day by going straight to the coast. Decide before departure. Returning a rental car in Split leaves the remaining journey free of island driving and parking.