Going in September

If I'm reading your plan correctly, you are traveling from Zagreb to Plitvice; back to Zagreb, and then to Rovinj? That involves some backtracking which will waste time. Most travelers advise that you arrive at Plitvice first thing in the morning to avoid the hordes of tourists and buses, so with a one day tour, be prepared for wall to wall people on those trails. We did not visit Rovinj due to the logistics of our trip, so I can not speak to that city.

Split was my least favorite place in all of Croatia. IMO it is highly overrated, and insanely crowded. If you feel that you must see it, then the very most time I would spend there would be 2 nights. I would suggest that you consider taking the ferry from Split to Korcula, and spend a few nights there. If that island does not interest you, then take a look at Hvar. From those islands you can ferry to Dubrovnik. We did not use the bus system in Croatia; had a rental car for a very small portion of the trip, and we also hired a private guide. It's a beautiful country, that you will enjoy!

It’s a full itinerary, but manageable without a rental car. Buses work well for most of it, and for parts where public transport gets tricky or time-consuming, private transfers are a good option.

After Rovinj, you’ve got 3 open nights, good places to consider are Zadar or Šibenik. Both are interesting coastal towns, well-connected, and less hectic than Split or Dubrovnik. Either makes a good stop before heading south.

In Split, 3 nights gives you time to explore and also do a day trip inland or along the coast. For transfers (e.g., Zadar/Šibenik/Split, or Split to Dubrovnik) and day trips out of Split, I recommend Ivan Ćosić (Mc-Travel Croatia). He’s a private driver based in Split and can help streamline things. Very reliable and responsive, you can find him on Facebook.

It can feel like a lot to plan, but having a driver lined up for the longer stretches or less direct routes makes it much easier.

I would recomend to stay in Rovinj who has one of the most beautifull sunsets
https://vm.tiktok.com/ZNdBVYpwn/

If you have time visit the rivers in Lika
https://vm.tiktok.com/ZNdB4ExcN/

or hidden lagoons around Pula
https://vm.tiktok.com/ZNdBVBWtg/

Why are you so resistant to rent a car? You will truly miss so much. The roads are fantastic in Croatia and driving is very safe. I would really recommend that if you go to Istria/Rovinj, that you have a car. Otherwise, what is the point? I suggest that you consider staying those extra three nights in Istria and really get to the know the place. So much to see.

At least you are willing to do Plitvice without spending the night. Good for you. It’s September and it will probably work out okay.

Emily says rent a car and Emily is a trusted source here. But Emily forgets that not all of us are comfortable driving on holiday; me included. Then there is the issue of either doing a round trip or paying a drop off fee that can be higher than the cost of the rental. But Emily might know a workaround or a company. Again, she is the best source.

I am a spoiled old fart. I only take holidays that I can afford to take to my standard of getting the most enjoyment possible out of the trip. I have done something similar to your plans twice and a shorter trip once. For your trip I would probably take the bus to Rovinj then use a transfer to Plitvice then a transfer to Split. It’s a long day, but worth it maybe. I love transfers so I can look out the window, yell stop and see things along the way and just plain not have to worry about anything, and no back tracking. Then a bus or a transfer to Dubrovnik.

How long in each stop? Well, the cities you mention are good bases to see a lot other than the city. So how many days is as much about what is around the city as the city itself. Otherwise I say 2 or 3 nights in Split and 2 or 3 in Dubrovnik. The best stuff in Croatia for me at least was the sorts of things where I needed expert advice and assistance to do well. Things like vineyards and olive orchards private boat trips. I generally look at Viator for each destination to get a list of the things to see and do then I contact a guide service and see if they can combine a few into something more enjoyable than a large group tour for a cost do. The 2 or 3 nights can turn into 5 or 6 that way.

I know a good tour agency in the region and I know a very good guide in Dubrovnik if either would help you.

Thanks so much for your reply.
My husband and I are 67 and 70 and really don’t want the responsibility of driving a car, parking etc… We also know taking a bus will allow us to enjoy the scenery. But know we don’t want to spend to much time traveling on the roads.
Can you share the tour guide company or a private drivers name and information?
Have a good day.

I sent you a PM with a few names.

Always happy to help. I wish I could help more with Croatia buy its a complicated place and to be helpful it takes good current and knowledgeable input and my few trips and few weeks in Croatia don't qualify. But the names I sent you are very, very good.

I trust Emily with northern Croata. I know she has a lot of experience.

Rovinj is the outlier, so if still considering bus travel I would consider eliminating it, as Zagreb-Plitvice-Split-Dubrovnik is really a snap by bus. This is a very standard itinerary and not complicated to do independently.
For the loose nights, add 1-2 for Plitvice, then pick an island between Split and Dubrovnik (catamaran travel is also a snap).