SANTORINI - If you arrive late (8pm ? 10 pm? ) I would advise not going into Central athens, but instead staying near the airport, (I can list 3 options at end) and flying out next AM (nov 19) to Santorini. Aegean has a 10:10am flight (45 mins) at €98. 1.5 days & 2 nights should be enough time appreciate the main attraction of Santorini outside of summer, the beautiful view of the Caldera. OIA is the place to take the most famous "postcard" photos, but of an evening, quite closed down ... best hotel location IMHO, would be a room with caldera view balcony, either in Fira Town or its Northern edge, Firostephani (which is an easy 15-minute walk along the rim path to Fira Town's cafes, shopping, museums). On day #2 take an early bus to OIA when the light is best for photos. Then you can go to the Fira Museum, and/or to Aktrotiri "dig" if underground ruins floats your boat. For a dinner in Fira Town with sunset views, check out STANI http://www.stani.gr -- its terrace floor has great views, and in cooler weather has clear plastic "walls."
Morning of Day 3 (nov 21), catch a flight BACK to the mainland; first one is 11:30 @ €94, arrives 12:15 ATH airport. (I know, airfare adds up -- but when you don't have time to spend you must spend €€€).
DELPHI & ATHENS -- You do NOT have time for Meteora, really so it's Delphi & Athens ... AND you must choose which to do first. If you wish to do DELPHI first, then you'll need to rent a car at Airport & drive there... it's an easy 3-hour drive, and you can then see the Museum at 4 or 5, and next AM tour the ruins in the lovely morning light. You cannot take an intercity bus because the only run is at 15:00 (3pm) arriving 5:30 and the site closes at 6. A nice modest hotel PAN, from its back rooms, has awesome views down the mountain to the sea (when we were there, hawks circled BELOW our balcony). If you position your Delphi trip as Friday-Saturday 24-25th, you could catch a 10:30am bus arr 1 pm, see most of the sight in afternoon, museum in AM, get 11 am Bus back.
ATHENS -- either Mid-week or at the end, you should enjoy 2.5 - 3 days in Athens which will be lively as any European Capital city is in the late-Fall edge of Winter. Besides the Acropolis, Agora & Acropolis Museum, there's of course the Amazing Natl. Arch. Museum with its fabulous treasures. You may wish a guided tour -- https://www.athenswalkingtours.gr is long-established and best-reviewed, has various lengths/prices. If you're D-I-Y types, Rick Steves website has step-by-step AUDIO for Acropolis, Agora AND the Nat. Mus, that you can download free from his website!! This website - http://www.athensinfoguide.com/open.htm -- is VERY outdated on hours & admission prices, but DOES show the amazing variety of museums, sites for EVERY interest .... jewelry, musical instruments, children's art, politics, pottery -- you name it, there's an institute for it! My chief tip would be NOT to book a big int'l chain hotel like Marriott or Hilton, they're not walking distance -- look at Hotels right smack-dab by Acropolis. Three moderate choices the S. side of Acropolis Are Hotels Herodion, Phillipos and Airotel Parthenon. NOTE: If your homebound flight is before 8 am you'll hve to be in line by 6 AM (even tho you'll then sit and sit and sit in departure lounge). It's 1 hr by bus to airport, 50 mins by taxi (and if you arrive before 6 am it's nighttime rate, nearly 60€). You may wish to consider being near Airport.
AIRPORT AREA Hotels:
Sofitel - ONLY Airport hotel, right across street but VERY pricey... $200+ even off season.
Holiday Inn Attiki - about 30 mins away, about $130-up. Has a shuttle but I don't know if early enough for your return flight.
St. Thomas B & B - v. nice $75 offseason, buffet breakfast (only works for you if u take that 10 am flight) 10-15€taxi, 15 min
Hotel Peris - Plain, clean, continental breakfast. $70? Used to have free shuttle, but not until 7 am; inquire before booking