Fast Trip - need Itinerary help

When you get to Zagreb after a ten hour layover in Paris, I suspect you will need to sleep before undertaking a long drive.
I'd play it by ear according to the weather for the island portion--if it's great, proceed, if it turns, stick to Split and maybe Zadar or Dubrovnik (not as a day trip--it's four hours away). Weather could go either way, but I think in mid October you don't have to have every thing booked.

We enjoyed staying in Zagreb for one night, and exploring the city center on foot the afternoon we arrived, and the morning after, before heading to a sobe near Plitvice. I’m very glad to have had that time in Zagreb. This was in mid June - I wonder what conditions will be like on the beach in October?

We had a longer stay in Split. Diocletian’s Palace was an amazing sight. What’s your daughters interest in Ancient Rome, and in massive palaces/castles in general? Didn’t make it to Dubrovnik on that trip. We had more time overall, actually renting car in Venice, driving to/thru Slovenia and Croatia, returning to Venice at the end.

10 hrs layover in Paris with a 4-5 hrs sightseeing of Paris?
What are the reality logistics on that?

Wow! What a dad! This trip will certainly go into your daughter's memory bank and you should score many brownie points.

Your daughter had been planning to see Paris until recently and then switched to Croatia? Is she sure about this? Does she need some guidance in her choices? If it were I, I would probably sit down with her and go over Paris sites and Croatia ones--she may be the type of kid who has already done much research and truly knows her mind. On the other hand. . .
What if your flight into Paris arrives late? What if you're both too tired to enjoy yourselves? Is there any chance you could spend at least one night in Paris?

This is great to go on a special trip with your daughter. I did it individually with my kids when they were young and it was so good for them to see a different part of the world.
However, I agree with a previous post that you are trying to squeeze too much into such a short time frame and why not just stick with Paris and really experience it? A few hours just isn’t worth it when you will likely be very tired, and then go back to the airport? I’m sorry but it just doesn’t sound like a good trip.

I think that it's lovely to plan a father/daughter trip.
If possible, try to spend one night in Paris.
That will give you a buffer against flight delay issues.
Leaving the airport during a 10 hour layover only gives you 4 or 41/2 hours in Paris itself.
You can do a quick overview of Paris (include the one hour Vedettes boat tour) and you can focus on one neighborhood, or two, for a walk-around and lovely meals.
I took the RS Best of the Adriatic a few years ago, and while I loved Plitvici I'm not sure it would appeal to a 13 year old girl -- It's a long day of walking/hiking on boardwalks and it's pretty hard (impossible?) to shorten the walk. Split, Hvar (to some extent), and Dubrovnik would be more appealing, I think.

This may not be the advice you want to hear, but with a week, and a child who has dreamed of Paris, spend a week in Paris. That would be a wonderful trip.

To clear up a few things:

• Paris - everyone is questioning either why we aren’t just doing Paris, or why we are trying to do a layover in Paris before coming to Croatia. My daughter from age 5 to about 10 had Paris as her dream destination. As she’s grown she’s backed off of that, and specifically requested something that’s more Island-y, or some beach time, while also still being European. I don’t want to do Greece because I want the whole family to go there in the next few years. That led to Croatia. She’s looked at Plitvice online as well as the islands, etc, and she’s excited for that.
  

Now, I understand that going in October it won’t be a tropical feel. But, that’s when we have to make this trip. It’s when her birthday is, and it’s just when it fits into the calendar best for the family.

I’ll talk with her more about the expected temps and propose Paris again, but this is what we’ve landed on.

At Plitvice there are a number of different marked paths of varying lengths, so you can pick a shorter option if you want to. On my most recent visit (2015) I chose the second-longest marked route and finished it at least an hour earlier than the posted time indicated--and I didn't get started until 11 AM on a day when the park was wall-to-wall people. I suppose they may have recalibrated those walking times since 2015.

Also on that trip I found the weather was becoming more fallish even as far south as Montenegro by around the beginning of October. I don't know whether that was unusual, but it is clearly possible. Except for (I think) October 10, the temperatures were very comfortable (I don't know about swimming), but I was getting a good bit of rain. The only really bad day was October 10, when I was in a very chilly, wet Zagreb. I bet it was milder on the coast that day; there's quite a difference in the average October temperatures for Zagreb and Split.

Honestly not trying to be Debbie downer but I really don’t get this forums obsession with Plitvice. A completely underwhelming site imo. Especially to spend 2 days at on a trip like this. Just my 2 cents. We had 3+ weeks in Croatia over a 3 month European trip and if I had known what plitvice was before going, I would have skipped it even with the ample time we had. Going to Krka is much more Central for your trip if you want to see waterfalls

October is the perfect time for Croatia. We spent 3 weeks from early to late October this past year and the weather was amazing. Swimming almost every day on Hvar, t shirts and shorts everywhere we went etc.

We only drove through split so it’s hard for me to comment on split VS Mostar, but that’s a decent drive both to and from. You trip already has quite a bit of time spent in the car so I may just stay in split or spend a day in another small town along the coast.

Mostar is certainly far more charming and a completely different cultural experience than you’d get in split but yea.. it’s a 2.5+ hour drive one way on top of stops, finding your accommodations etc.

According to ViaMichelin.com, driving Zagreb - Plitvice Lakes - Split takes just about one hour longer than driving directly between Zagreb and Split. You can see a lot of the park in just a few hours, so adding that stop needn't take even one full day out of the itinerary. You could spend the morning in Zagreb before heading to the lakes. On the second day you'd probably finish up really early and could be in Split by around noon--maybe earlier.

The trick is not to see the park along with all the day-trippers. It definitely loses its charm when you're marching shoulder to shoulder (and toe to heel) with thousands of other visitors.

Enjoy the morning and lunch in Zagreb, before you drive to Plitvice. We did. There are some wonderful small scale sights, there. The Naive Art Museum, the shopping district just below and to the east of the Upper Town (and just north of Jelacic Square). There's also the Museum of Broken Relationships.

Your day from Plitvice to Split and then on to one of the islands sounds overly ambitious. Since you plan to spend some time in Split anyway, why not do it earlier on your trip (Night 3, Day 4, Night 4?), rather than at the end? That will give you a little more time to enjoy Plitvice for a full 1/2 day. It's worth spending some time there and walking some of the many trails among the lakes and falls. You may have a little time on your drive to Split to stop at Sibenik or Trogir (or Zadar or Krka?) to break up the trip to Split.

Then after Day 4, you would spend Days 5 and 6 on one of the islands, and back to Split for the final night 6.