Advice on itinerary in Croatia

Sept. 2-5. Dubrovnik

A bit long to linger in Dubrovnik, IMHO. The city itself is compact, and unbelievably crowded during the day when cruise ships dump their thousands of passengers. One day is enough for me. That said, I'd take one of your days and do a day trip to Kotor.

Sept. 5-8 Hvar

Do you want to spend your trip clubbing all night and getting baked? If so, 3 days in Hvar town would be perfect. Otherwise...you might want to consider at least some of that time elsewhere (get out of Hvar town to somewhere else on the island, or better yet, skip Hvar and go to Korcula, which I liked much better).

Rab and Rovinj are great. But you're planning to entirely skip Split and Plitvice? You might want to give that some thought. Plitvice is certainly worth a stop.

Depends are a few factors, where is your next stop after Croatia or are you flying home from there. That said, which airport. How do you plan on getting from the south to up north? In my opinion, not too long in Dubrovnik. The city has a few good museums, which are always empty, and Churches to visit, plus walking the wall takes a few hours. You can spend a full or half day on Lokrum island which is a nature preserve with a few ruins and a very nice cafe near the pier. You can also go swimming (if on the first ferry of the day, follow the old people to the best beach on the other side). They also have a nudist beach if that is your thing. Or you could kayak over to Lokrum. Definitely take a city walking tour as the history is very interesting.
Don't bypass Split. A total different feel then Dubrovnik and if you are just coming from Greece you will appreciate the history. You can easily day trip from there to Krka National park or to Trogir, a compact city also with an interesting history.
Korcula is a personal favorite and great for a day or two. You can ferry from Dubrovnik to Korcula then Korcula to Split. The ferry from Korcula to split also stops at Hvar if you wanted to stay a night or two. All tickets can be pre booked.

I do not think that 3 nights in each location is too long, actually about right. Yeah, you are missing Korcula between Dubrovnik and Hvar, and Split between Hvar and Rab. But you will pass through Split and could spend a half day there easily.

Yes, from Dubrovnik you could venture into Montenegro and Kotor, but with only two full days...Dubrovnik is good. Same with Hvar, you could hit some islands, we rented a small motorboat and cruised around some of the small islands, snorkeled, did beach, got naked on one of the islands, but just relaxing on Hvar works as well.

Some of the response you will get is since you are proposing a conservative schedule, many will propose another 3-4 stops, if you propose 6 stops as opposed to 4, they will tell you to cut back. Stick with simpler, there are no "must see or you will die" places, only your interests, and the fewer the better.

You are brave seeing Greece in August! Hot hot hot.

IMO you are trying to cover too much ground in your timescale.

I would be tempted to take a day from Dubrovnik and add it to Rovinj.

At that time of year, Hvar town will still be in full party mode, so if you want peace and tranquillity, head to Stari Grad or Jelsa, not Hvar town.

Have you looked into how you are going to get from Hvar to Rab? This isn’t a short journey - 8-10 hours plus assuming you won’t have a hire car. It’s not a journey I would want to make for only 2 full days there. I would change Rab to Split, stay 2 nights and see Split and Trogir. Either have a night at Plitvice or add another night to Rovinj. The hill towns themselves deserve at least 2 full days, plus there’s the coast.

You should be concerned about transportation between each city. You are looking at several full days of travel. You are looking at spending 25% of your time on the road. The Rab portion makes logistics very complex as well. We liked Brac better than Hvar. Consider Split instead of Rab. I'd rent a car from Split to Rovinj and use the car while in Istria.

Paul makes some good points--you don't want to go too fast and try to cram too much in, but then again, without knowing your interests, the reasoning behind your choices, what day trips you wish to do, or your transport preferences, it is hard to advise.
Though Dubrovnik is small, and yes the cruise ship people are intent on ruining it for everyone else, it is only two full days, so I would keep that as is.
I have only been to Hvar in May, when it was nothing like what I hear it is in July-August. If that party vibe extends into early September, then I would prefer Stari Grad (or try Korcula as suggested).
I would at least spend an afternoon in Split to see the palace.
I have not been to Rab, but getting to the less popular islands is something I highly recommend--it has made for some of my best trips in Croatia when I did so.
I have not yet been to Istria (which is a great destination for September and October), but I would want more than two nights in Rovinj. Without more time to explore the hill towns, there is no need for a car, but getting there will be a time-consuming pain without one.
Where do you fly out from?
For catamarans and ferries, see the Krilo and Jadrolinija websites.

I agree that Istria can be a bit difficult to get to by public transportation, and onward travel will probably take extra time as well. I wouldn't go for just two nights, probably not for just three. I enjoyed a one-day bus tour of inland Istria (offered only on Wednesdays as of 2015). I based in Rovinj and took side-trips to Porec and Vrsar. Without a car, accomplishing all of that took about three full days. Pula would have added more time.

We go to Istria every Easter for a week and still haven't seen everything. Such a pitifully short time in Istria on this itinerary.

If you take the catamaran from Zadar to Istria, your travel time will be minimal compared with the bus or car.

I really appreciate all the great comments on my Croatia trip. I wanted to answer a few of the comments.

After we leave Rovinj, we travel to Düsseldorf Germany to see relatives. We are flying out of Pula. We then travel to Munich and catch Octoberfest and then back to the states.

We do plan to cut a day out of Hvar and one from Rab and add this to Split. My thoughts were to rent a car after I leave Split and drive to Rab and then to Rovinj. My other option would be to stay at Zadar one night and take a Catamaran to Pula. This would mean cutting out Rab. Is Zadar a worthwhile city to visit? I do have a couple extra days That I could stay at Rovinj since I have not secure my flight yet. This will be completed within the next two weeks.