Help! Too much to do too little time!

I am out of breath from reading it .... couldnt do it. But looks amazing for someone younger. Have a blast.

A few thoughts...
1) Have you taken into consideration the cost of the rental car's drop off fee since you are renting in Slovenia and dropping it off in Croatia? There is normally a hefty price tag on doing that.
2) Split is my least favorite city, so if I had to eliminate something because of PTO it would be that.
3) You have less than a full day to spend in Dubrovnik; IMO that's not enough time to "explore" there.
4) It poured rain the entire day we were in Plitvice. So between that and the hordes of people and tour buses, it was absolutely miserable. You may want to consider pivoting on that day, and have an alternative plan in mind in case bad weather is a factor.
5) We loved our stay on Korcula! The hop on-hop off water taxi was great; walked to some wineries from the Lumbarda stop; watched the Moreska Sword Dance performance.
Enjoy your trip!

Have you scoped out the driving distances and have some idea of how long the transit
between each stop will take?

For instance, it's about 3 hours from Plitvice to Split. Per your schedule, that gives you
a half day to explore Split. That might be enough for some people, but is it enough for you?
Same for Dubrovnik, you've got essentially a half day. It also sounds like you would skip
the pass in favor of the highway to go from Bled to Rovinj, which I wouldn't do. If you
weren't, there is no way you can go from Bled over the pass, see the caves/castle, and
get to Rovinj in one day, unless you don't stop anywhere.

This sounds drastic, but I'd consider cutting out Split and Dubrovnik and the islands entirely.
From Plitvice, head back to Zagreb and fly home from there. Split/Dubrovnik/islands can
be it's own trip another time, add in Mostar or something else in that area.

I agree with shoeflyer. If you add a night or two to Rovijn you could explore Istria with the car - Poreć, Grožnjan, Pula, Hum (world’s smallest town), Oprtalj, etc.
You could then visit Zagreb after Plitvice and circle back to Ljubljana to return your car. Maybe even stop in Samovor for the best kremšnita and šampita cakes.
Ljubljana is a short drive from Zagreb.

The south could definitely be another trip cause you could add in Sarajevo, Kotor, etc.

Plitvice Lakes National Park is beautiful but totally swamped by daytrippers. The only way to really appreciate the park is to see it in the late afternoon and/or first thing in the morning. It's essential to spend a night in or very near the park so you don't have to deal with hordes of other visitors. Please believe me. I recommend skipping Plitvice on this trip if you can see it only during daytripping hours.

The good news is that you can see a great deal of the park in 4 to 6 hours.

Hi JeanneS, Welcome to the forum. After being to both Slovenia and Croatia and planning a return this September—here are my thoughts: Stay the two nights near Lake Bohinj rather than Bled. Ribcev Laz is a good base town for Lake Bohinj. There are miles of hiking all around the turquoise lake and in Mostnica Gorge here—and you’ll be inside Triglav National Park—which Bled is not. Lake Bohinj is not overcrowded— which Bled definitely is. The two are just 30 minutes away from each other—yet world’s apart.
Then see Predjama Castle and SKOCJAN CAVES (1-2 hrs from Ribcev Laz) before driving onto Rovinj. (2 hrs further).
To simplify your itinerary, you could substitute in the Venetian town of PIRAN in Slovenia for the Venetian town of Rovinj in Croatia. It would spare you hours of driving. Piran is just 35 minutes from Skocjan Caves. After Piran it is an 80-minute drive to Ljubljana if you decide to return the car rental within Slovenia.

If you are going to Plitvice Lakes National Park, stay overnight so you can visit during the afternoon on the day you arrive after all the daytrippers have left and again the next morning at 7am before the hordes arrive. You can buy a “Two-Day Ticket” for €60.
You can then drive to Split and see Diocletian’s Palace— the main reason for stopping in Split.
Return the rental car in downtown Split if you can because you can take the Krilo catamaran to Hvar Town (1 hr) from Split’s ferry port right outside Diocletian’s Palace. Then take the 90-minute Krilo catamaran from Hvar Town to Korcula Town. The catamarans are the only boats that dock in Korcula Town— the ferries go to another port miles away.
Finally, take the two-hour Krilo catamaran from Korcula Town to Dubrovnik. There is another high-speed boat called the TP Line that might work as well.
www.CroatiaFerries.com has schedules and sells tix.

In order to avoid the one-way dropoff charge of 600 euros next September, I’m renting a car in Ljubljana for the time in Slovenia and then taking the train to Zagreb where a different car will be rented for Croatia. The two capitals are just 2-3 hours by bus/train from each other.

Have fun exploring Slovenia & Croatia!

Lots of good advice here OP. I think Kenko’s plan is pretty comprehensive. I’m assuming your airfare is locked in, so will leave that alone.

I’ll just throw this out there. Rovinj is a logistical outlier that really complicates just about every itinerary I see on this forum. IMO, leave it out. If you cut Rovinj from the itinerary, your path keeps you much more north-south. You’re squeezed from the jump, and this is not helping. Hvar, Korcula, and (potential crowds side) even Dubrovnik can deliver the same coastal beauty and tranquility. Basically, it seems every beach in Croatia is some level of stunning, and that old Venitian port ambience is not unique. Dropping the hassle and cost of the car in Split, then using your Rovinj days on this stretch makes more sense to me.

And if you’re scraping for days, I also see no problem heading right to Dubrovnik for the last few nights and passing by Hvar/Korcula. Dubrovnik has myriad options for activities. And a day on Lokrum for swimming stacks up against anything in those smaller towns.

Lots of good options and advice offered. The only additional thought I had is that I see you spending 2 nights at Plitvice. If you need to cut a night, on Day 6 you COULD leave in the morning and spend the afternoon in the park at Plitvice; spend one night there; then spend the following morning; drive to Split in the afternoon. Depending on ferry times, you then might spend the morning and early afternoon in Split, getting on the ferry late afternoon. That is plenty of time to see Diocletian’s Palace.

However if you skip Rovinj (and sub in Piran instead for 1 night), you might not need this solution. You would gain your extra night that way.

If you must to do Plitvice lakes, then start off on the trip there late or find some interesting stops along the way so that you don’t arrive at the hotel until late. Trsat Castle and the town of Rijeka are an option. Why? Cause that night in Plitvice will be a Motel6 sort of experience. Then get up early and get to the park with the ticket you bought online a month in advance and get it over early and head on down the road to Split. The trouble with trying to make a late afternoon visit is sunset in mid-September is 7pm. Add the night you save to Dubrovnik (although you can spend the day out of the city).

I only have one experience with Plitvice. I arrived about 11am in July and it wasn’t bad at all. But everyone tells me it was a fluke, or it was too close to COVID, or it just doesn’t happen that way cause the internet and AI say ...... I will say that by noon it was a zoo, and I wanted out. Here is some more poop: https://www.kvntravel.nl/en/europe/croatia/plitvice-lakes-high-season

Have you considered the use or a using Slovenia explorer to help with your trip to stake the stress out of driving and the hassle? We are looking at visiting Slovenia for a trip and I don't want the hassle of driving so we are looking at this option. You could take one of their packaged trips or have them design one from what I see. We are still in discussions with them so I don't know the pros and cons or potential costs at this point.