If you have such a short trip, every hour matters & going in to Athens 2x uses up precious time. For trip-lengths like yours... and even longer ... old hands always suggest on arrival day to fly immediately to the farthest destination & work your way back. Santorini has the most flights ... if you fly a nonstop from N. America, those 4 always arrive between 9 & 10 am --- allow a couple hours to deplane, get thru passport control, pick up baggage, get a few Euros from an ATM .. It's all one big building so u just walk from the international-airline end to the domestic end. Piece o'cake. If you arrive by 10 you can get a noon flight to Santorini (only 50 mins vs 6-9 hours on ferry), and can be sitting on y our balcony admiring the view by 2 pm... You may be able to save a few bucks by a flight plan that changes planes in Europe, but then u likely will not arrive until 2pm earliest, and latest, by 5 pm. On a brief trip, because u can't spend time, often u must spend money. It's a trade-off.
We'd be able to suggest better, if we knew your motives for each destination. Are u mainly goig to Santorini because it is famous? Is swimming part of your plan there?? When u do homework you will see that beaches are definitely so-so there (black grit) and the Main Attraction is the Famous Caldera View. Splurge on a cliffedge hotel for that --, and unless u want to do splurge-y add on s like caldera cruise... maybe shorten your stay by 1 night.... leave on 3:15 Blue Star Ferry (2+ hrs) to Naxos. then u could have 4 nights on Naxos --- which has the most variety of sights & activities (beach, hiking, ruins, landscapes, food tours etc). Fly from Naxos back to Athens (45 mins vs 6 hrs ferry). Do Athens last... after being in Greece awhile the famous capital landmarks resonate so much more, and museums as well.
Meteora is too far out of he way for such a short & First trip... save it for another year. If you fly from Naxos and arrive by noon or early afternoon it would be SO easy to add a good Delphi experience. Pick up a rental car, and drive straight to Delphi arrive late afternoon... y ou can check into a modest hotel with view down the mountain... and visit the museum at 6 or so, when No One is there (very good signage easy to understand), have a sunset terrace dinner with a glorious view. Rise early and be at the ruins site by 8 am and y ou'll have 2 hours before all he bus tours arrive, & by that time you'll be high up on the hillside, ahead of the throng.
Drive back noon-ish, drop the car at Airport & taxi or express bus to a central Athens hotel.
NOTE: if you have no ancient-greece background & don't plan doing any "homework" before trip, you might get the most of Delphi using a licensed guide (but they are pricey). There are many many excellent websites to study & print out as an alternative.