5 nights in Croatia dilemma

I was in Croata & Slovenia for a month last year. I loved all of it! Some suggestions:
Split -If you can - stay somewhere inside Diocletian's Palace, esp. if only one night, the palace is very nice @ night. And the walking distance down to the ferries is not too bad.
Hvar- It depends on if you are going to Hvar to live it up, i.e. nightlife, if so it should work. I am a quiet person looking to relax so I went to Vis instead. I loved it. But true there was no nightlife....

Have a great trip,
Curly

With only 5 nights (4.5 days), I wouldn't choose itinerary #2 as it involves a fair amount of travel time. Focusing on Dubrovnik and nearby Montenegro makes more sense to me. There are a few possibilities for beach time in the area. My recollection is that Budva in Montenegro had some nice beaches, and it could work as your night 2. In Dubrovnik, I remember seeing a small beach club just a short walk south of the old walled town and some of the hotels in Lapad may have nice beaches. You can use Google Maps to get a preliminary idea of whether any of those beach options could meet your needs.

Beaches in Croatia are often the pebble/rock sort. In Dubrovnik, there is no sandy beach. In Cavtat (1/2 hour boat ride), there is one, I believe. We're not beach sitters, so it's not big on our radar.

As to 5 days in Croatia, stick with Dubrovnik, and do day trips. You can go to Cavtat, Kotor, and probably hire a car to go to a farm restaurant in the area. There are islands near Dubrovnik, and some "islands" are really peninsulas.

Just checked - no sandy beach in Cavtat, but there is one on a local island. Sandy beaches are less common in Europe. That being said, there is an excellent, large, popular sandy beach in Split.

Google "sandy beach dubrovnik" for more thoughts.

And you do not indicate how you are getting to Kotor. There are 3 options: rent a car, hire a driver, take the bus. For just 1 day, it seems like it might be expensive to rent a car.

Sandy beaches are less common in Europe.
Ahem what now? Europe has an enormours coastline with thousands of kms of sandy beaches, what on Earth are you talking about?
But yes, Croatias beaches are more Penbbly than sandy. Personally I wouldnt go all the way to Hvar just for sandy beaches. But I might have a personal grudge since I steppes on a Sea urchin there.

You may consider Brač (island) instead of Hvar. Zlatni Rat beach near Bol (on Brač) is stunning; the sand is fairly soft. It's quite popular and crowded though because it is so beautiful.
https://en.wikipedia.org/wiki/Zlatni_Rat

I'm unclear on whether Croatia is your first stop in Europe (after an overnight flight) or whether you will simply be arriving from somewhere like Germany. If you're arriving after a transatlantic flight, I urge you not to plan to rent a car and drive around the Bay of Kotor that day. It is a glorious area, but that would not be a safe drive for a sleep-deprived/jetlagged driver. Even for someone fully alert, the views are such that it might be a bit of a challenge to keep ones eyes on the road. (I took a bus.)

If I had just five days in Croatia I wouldn't be spending any of that time lying on a beach. But then I don't go to beaches in the US, either.

Depends on what kinds of beach you want, but you could stay in Dubrovnik and day trip to some of the Elafiti islands.
What time of year?

I'll be there the first week in June. Elafiti islands sound compelling for a day trip. I will look into it. Is there a specific island you would recommend?

Thanks!

I have not been to Elafiti, only know that there are nice beaches.
For ferries and catamarans:
http://www.gv-line.hr/raspored.php?linija=3&lang=E
https://www.jadrolinija.hr/
https://www.krilo.hr/en/

I went to Kotor but did not see a nice beach around the bay. At Budva, there is a sand beach but it was pretty crowded. I think on the islands you can spread about a bit, find your own little cove.
You might want to check Mljet also.

Šunj beach on Lopud (one of the Elaphiti Islands) is a stunning sand beach that you can reach as a day trip from Dubrovnik. It's regularly referred to as one of the best beaches in Croatia and I can understand why! I spent five days on Lopud swimming and walking and it is an absolutely perfect place to relax.

There are also great beaches around Dubrovnik, though not sandy ones. You can walk to several around the city or take the boat over to Lokrum and swim there.