Croatia/Slovenia itinerary
 

Comments:
Sept 9 Lv Vienna for Zagreb
Spend Sept 9 and 10 in Zagreb
On 11th head for Plitvice Lakes National Park
Visit Park in 12th and head for Split
Spend Sept 12-13 in Split
Sept 14 head for Dubrovnik
Sept 14-15 Dubrovnik
Sept 16 head for Istria
Sept 16-17 in Istria
Sept 17 head for Ljubljana
Sept 17-18 Ljubljana
Sept 19 head for Lake Bohinj
Sept 19-21 Lake Bohinj
Sept 21 head for Kranjska Gora
Sept 21-23 Kranjska Gora and head for Vienna to spend the night for 24th flight home

Perhaps I have already suggested this(?) - but have you considered flying from Vienna to Zagreb, renting the car there, returning in Dubrovnik, and flying back to Vienna from there? That would cost a little more but would save you 9+ hours of driving all the way back to Vienna. (And would save you the drive from Vienna to Zagreb.) Then you could weave your way from Zagreb to Dubrovnik with a detour through Slovenia.

Some people love to drive too, I suppose.

Have you already booked flights? Trying to start AND leave from Zagreb makes your plan more complicated than it might otherwise be. If you could fly into or out of Dubrovnik,, you might be able to simplify your trip. In that case, your sequencing might be something like Vienna through Slovenia to Zagreb to Istria to the Plitvice Lakes to Split to Dubrovnik and out. (Or vice versa.)

The timing really depends on YOUR interests, but FWIW, I think you are cutting it thin. You will loose a chunk of time with each change of location, so, for example, you don't really have 2 days in Zagreb -- you have 1 and perhaps parts of two. You don't have 2 days in Istria -- you have a night there. Etc. I encourage you to lay everything out on a calendar: The time you will spend in transit (and I don't think you said how you plan to travel?), the time it will take to check into / out of hotels, time for meals, time to see and experience whatever it is that YOU want to see and experience.... Then see how things fit together.

BTW, have you seen our responses to your earlier posts? You need to click on your name to find them.

Good luck!

Cannot comment through Sept 15 but the rest of your planning looks good to me. We just came back from a 10 day trip to Slovenia and Istria and spend an avg of 2 days in most places and the pace was just fine. Our itinerary was as follows

Vienna
Day 1, 2 - Syria wine region
Day 3. 4 - Logarska Dolina
Day 5, 6 - Bled and Bohinj
Day 7 - Vrsic pass, Soca river valley (stayed in Bovec)
Day 8, 9 - Piran and Istria
Day 10 - Ljubljana
Day 11 - Vienna

We loved all of Slovenia. Simply stunning country with great friendly folks and good food. Vrisic pass and the Soca valley are stunning as is the logarska dolina region. Ljubljana is a lovely city and can be covered in a day or so.

hello

Sept 17 head for Ljubljana
Sept 17-18 Ljubljana
Sept 19 head for Lake Bohinj

It is not often the case, but you factored in too much time for transfers :
Istria - Ljubljana is 2 hours (+ finding your way, so 3)
Ljubljana - Lake Bohinj is 1 hour top - did it last week.

Ljubjlana doesn't require 2 days - 2 evenings and one full days is enough - you can skip the castle imho, we went there 4 of us (40+, 14, 5), and nobody found it worthwile.

Lake Bohinj : there is a nice boat you can take and a climb to ? with a telecabin.

Regarding the Ljubljana castle: the views down from that castle grounds are terrific, so at very least, walk up there on a nice day (or take the funicular).

Lake Bohinj - cable car to Vogel is a must. Gorgeous. Once up there you can take another chair lift or hike up.

In Istria our favorite little town was Groznjan. Kozlovic winery is excellent as well (in momjan). We sat outdoors and the experience was one I will remember for a long time. All of this is easily doable in one afternoon.

if driving...GPS is a must...we found ours invaluable.