one day in Santorini

Hire a car and driver to maximize your time. Contact Gabi Birbeck on Facebook in the "Santorini Secrets" group. She lives on the island and provides this service as well as others. Oia is definitely a must-see. Also go to the amazing archaeological site of Akrotiri. Have lunch below Oia on the wharf in Amoudi Bay. Your teens can jump off the rocks at the end of the seawall that begins there. This is what it looks like down there: https://tinyurl.com/2cmza5jx
Amoudi Bay cliff jumping: https://tinyurl.com/msu9aj67

Since you arrive 1645 (4:45pm), you will have oppty to have a nice sunset dinner 1st night in Fira - I recommend rooftop of Stani Taverna (have your landlord mark it on map), good view from tables, theyll honor a phone res, wide variety of Greek cuisine, AND Affordable prices. Yes, see OIA, but get an EArly Start!! to beat the huge cruise crowds & package tour armies. With 4 of you, hire car for delivery to yr hotel by 8 am (drag those teens out of bed!), & get to OIA By 8:30 latest... then you'll have about 2 hours to stroll the lanes, take all the pix... until the huge throngs arrive & jampack the lanes. That's your cue to leave...

What next? if u are archeology buffs, you can go to Akrotiri, with a good map/info from guidebook or internet to make sense of ruins; sometimes there's a licensed guide at entry making up a group @ €10 a head but don't count on it. What next? U can walk nearby to see Red Beach but don't go there (dangerous; rockfalls). Don't use yr time for Santo Beaches (black grit) -- instead, how about a high high Bluff with fab view? Ancient THira... Drive to beach town, drive up wiggly road then goat-path to top -- u can see whole island!

What next? There will be a nonstop mob-scene in center of FIRA town but of course head for the clilff-edge promenade, starting at the Cathedral & walk North -- at edge of Village (near Cable Car exit), is NOMIKOS Conference Center. https://www.santorini.com/exhibitions/nomikos.htm It has a terrace with stellar views -- but inside, ALSO amazing exhibit of the AKrotire murals from 3,000? BC. originals are in Athens Museum, but these authentic realizations in cave settings are stunning, for appreciation of very advanced (and mysterious) civilization buried by a volcano. What next? IF the teens want exercise -- walk DOWN The steep steps to the harbor (hopping over donkey-poo). Since the "cruisers" will be mainly taking the cable car DOWN, you can probably easily get an UPward-bound car ... then go find another good restaurant for dinner... having had a good sample of Santorini.

NOTE re Souvenirs - After many Greece trips, I've learned to choose carefully. Don't load yourself down with "generic" souvenirs at each stop (Calendars, playing cards, "evil eye" trinkets)... u can get them at end of t rip... just get what's unique to each place - like Santorini, something made from lava?

We did a similar visit with our two kids. We stayed in Oia and loved our dinner at Santorini Mou. I think Oia is spectacular as did my teens. We just wandered around and watched the sunset. Our week in Naxos was heaven. Wake up, beach, dinner, repeat for 7 days.

We stayed in Oia, pretty to look at but gets so very crowded. We had great views from our balcony.
Our two favorite things we did in Santorini were hiking down to Amoudi Harbor for a seafood lunch and visiting Akrotiri , the ancient site where you will learn about the history of the island, including the volcanic eruption, 1600 BC. We rented a car for a day and it was delivered to our hotel, picked up there too.

We used Touring with Kostas and chose the "A la Carte Tour" https://santorini-private-guide.com/ After doing some research on my own of things that interested us, I contacted Kostas and bounced some ideas off of him. He then made some suggestions and we came up with a touring plan that met our needs.

Travel Bug, is Kostas a licensed guide? If not, I expect he just gave you a folder of some type when you went to the Akrotiri RUins or to the Santorini museum. Without certification, a guide is legally not allowed to escort you through ruins or museums or historic places. I am sure that he is a very knowledgeable driver, and if one is not that interested in archeology or Minoan culture, a tour driver can take you to all the highlights.

Janet,
As I stated, we worked with Kostas to plan a day that met our interests. We did not wish to visit Akotiri or any other museums. If you read the OP's original post carefully, they did not ask for a "licensed guide". Hence my recommendation. It's interesting that you frequently feel the need to point out what you perceive to be mistakes in other travelers' suggestions. All of us are on this forum just trying to share and gain new ideas.