OneCanadian, another possibility is a night at the airport Sofitel followed by an early morning flight to Naxos or Santorini. You won't do much after your 9 pm arrival even if you stay in Athens, so why not get a good night's sleep and hit the floor running next morning?

After a sleep in Sofitel's comfortable beds, walk across the street to the terminal and catch the 6:25 am flight to Naxos. You will arrive on Naxos at 7:05 am ready for a full day on the island. It will probably be too early to check into your Naxos hotel room, but you can drop off your bags, have breakfast, and come back later.

Sofitel is expensive, but I've stayed there a couple of times before early morning flights and feel it is worth it. It's only a five minute walk between the terminal and hotel reception, so you can be in your room shortly after you pick up your bags from the Arrivals carousel. Next morning walk across to the airline check-in desk.

I agree with Heimdall about staying one night in Athens and getting off as early as you can in the morning - if you can get an early morning flight and the Sofitel is too expensive try Peris Hotel near the airport. They will pick you up from your flight and drop you back in the morning. It's comfortable and friendly and much cheaper.
I also advise flying back to Athens when you have such a limited time. We were in Greece earlier this year at the time of the ferry strike (which started at 2 days and extended to 4). We saw lots of people really having problems while we simply got our flights... I love the ferries but it's not the best use of your time when your days are soooo limited. Santorini and Naxos are good choices for your first two islands... no doubt you will be back and you can try some of the others then.
I never thought of an airbnb in Santorini - be interesting to know how you go.

ps - in Naxos try Lucullus restaurant up in the castro... we keep returning again and again...

pps - and a great boat tour to do is from Naxos to Delos and Mykonos - lovely day trip to a) a fascinating spiritual place of historical important and b) a gorgeous tourist trap... two sides of the Greek islands.

Thank you, kja, yeshekathy, and heirndall again. Much to study here. Truly appreciate the restaurant suggestions. I'll likely be back with more questions in a couple of days! May have to rework my thoughts completely with the "stay near the airport, fly to Naxos early next day" thought.

Between Athens and Santorini, where would you spend your anniversary? Given my draft itinerary earlier, I had my wrapped around spending it in Santorini....

As someone who is not fond of mornings, I would rather push on once I arrive somewhere than stay over to face either an early morning flight or a loss of time on that first full day. I think it would depend on the exact timing, and I suspect we each have our own preferences about pushing on or resting first....

Kja, I agree, but the OP is arriving too late to push on to an island that night. There is a midnight ferry from Piraeus stopping at Naxos, then going on to Santorini, but its last sailing is on Sep 9th. That leaves the OP no alternative but to stay at or near Athens the first night.

My concern is meeting the connection back to Canada coming directly from an island. I have done that many times myself (going back to the UK) without a hitch, but on my last trip to Greece missed my connection for reasons I won't get into. The rearranged flight to London was more expensive, but not, I'm sure, as costly as a missed flight to Canada.

The beauty of staying at the airport Sofitel is: you can be in your room 15 minutes after picking up luggage from the carousel, then be at the airline check-in desk next morning 5 minutes after checking out of the hotel. With an early flight to either Naxos or Santorini you can be on the island around 7 am, probably before you are even out of bed had you stayed in Athens. Yeah, that means getting up early, and there are later flights to the islands if you prefer to stay longer in bed.

Sorry -- I missed the information about the time of arrival in Athens.

Hello everyone, thank you again for all your time and insights. I'm sure you'll now sigh as I've still gone and done a bit of my own thing. Heirndall, I very much appreciate your concern (and others') about us missing our flight back to Canada, but I'm a bit of a risk taker and optimist and so, have decided to take the chance and come back from Santorini late and hope to catch our flight back home OK. So, the overall plan is ...
Wed - Arrive Athens late (stay airbnb near Acropolis Museum)
Thu, Fri - Athens
Sat - mid-morning flight to Naxos (stay Pension Sofi)
Sun - Naxos
Mon - early afternoon ferry to Santorini (stay Noni's Apartments; left it too late for airbnb)
Tue, Wed - Santorini (our anniversary is on the Tue)
Wed 10pm+ - flight to Athens (stay Peris Hotel)
Thu morning - flight home
Fri-Sun - recover!

As I've learned more, I'm considering this our "dip toes in Greece" trip. We'll have to be back.

I have heard that A is for Athens has a bar/lounge with a great view; it's also been recommended for dinner. Any thoughts on it or another restaurant with the view and good food?

Also, still trying to determine where we should have a sunset dinner in Santorini on our anniversary. All recommendations would be much appreciated!

Are the boat/cat tours in Santorini worth the $$? They seem pretty pricey to me.

Thanks again to everyone!

IF you are worrying about prices, you won't want a hugely expensive sunset dinner - but you do want something with a good view, where y ou'll be treated specially. Since you will be staying in Fira town, you won't want to be going up to Oia ... and in Fira Town I know of a fine place: the rooftop terrace of STANI http://www.stani.gr This place is 1 or 2 lanes back from the caldera rim-path, and its roof terrace has a SPLENDID view. I suggest you stop by during the day, and select the table you want to reserve ... they WILL save it for you, unlike some Santo restaurants (but DO get there on time). Tell them it's your anniversary, and I know you'll get special treatment.

Sunset is about 7:15, so you'll want to get there about 6:30 anyway. How to get there? Ask your hotelier. I think the easiest way is to take the path to the Atlantis hotel next to Cathedral, follow that rimside promenade until a little before the Cable-Car, then turn inland. Your hotel can mark a map, or tell you a landmark to look for (Greek isles have no street signs or numbers!).

Forgot to say, STANI serves traditional Greek cuisine, very well-prepared, not a "fawncy international menu" ... and you'll be hard put to spend more than €15 each for LARGE meal, aside from beverage. the "House White" should be very good ... Santorini is justly famous for its Assyrtiko whites -- dry, fresh, intense, slight citrusy touch .

Thank you, traveljan! I will heed your advice for our anniversary. That's wonderful info. We'll love traditional food, no need for fancy for us. Tasty is what's important!

You mentioned Oia. We will do the hike to Oia, but probably leave Fira in the morning and get there for lunch. Any recommendations there? Thanks again!

That's absolutely fine that you didn't take my advice, OneCanadian! Sometimes I ignore it myself, but would never suggest that someone else take a risk. I've gambled many times on same day return to Athens, and only once missed the flight home. I would feel awful if you missed your flight back to Canada if I gave you the wrong advice.

I appreciate your thoughtfulness, Heirndall, I truly do. I could just imagine our anniversary dinner in Santorini, watching the sun set, and couldn't give it up!

"- in particular, can you recommend a wonderful restaurant in Santorini - with "those views" for dinner, as we'll be there for our 3rd wedding anniversary and I want to make the evening special."

We stayed at a hotel on the caldera, near Imerovigli, a location we highly recommend. Best sunset views, without the crowds at Oia.

Late September is when we visited, and the weather does start to turn rainy at that time of year.

We LOVED this little restaurant: La Maison (ignore the French name; it's not French cuisine)
http://www.lamaison-santorini.com

It sits right on the wonderful walkway along the caldera, that is magical at night.

I don't know where your lodging is, but for a romantic evening, I suggest you start at Imerovigli and walk to/from the restaurant.

PS. Make reservations for La Maison, because it is very small.

I see that you say u are flying back from Santorini to ATH airport on Wednesday night ... if you should decide to do Wed. afternoon, that might ease Heimdall's concern; you would know if there were some big flight glitch, you could still make the 19:30 (7:30pm) Seajet 2 -- it's NObody's choice of ferry (small, bouncy) but a disaster-avoidance fallback.

Regarding Fira-Oia Hike, I'm not a great fan of it... I'd rather enjoy the view sitting in a cafe.. why not hike instead on Naxos ... On this website http://www.cycladen.be/NaxosEng.htm -Hike #15 is a great short one, straight up from Port along the Grotta bluff, to a monastery high above port, great place to see sun get lowish at 6pm, then descend to portside taverna for meal, hike is about 30-45 minutes each way, enough to whet appetite, whereas that FIra-Oia hike is like, 5 miles. It's mainly promoted by Santorini-buffs, because it's just about the only hike on the island (vs 30-40 choices on Naxos).

RE MoBro's recommend - Lamaison Website looks lovely, sort of cuisine moderne Luxe type - one reason I suggested Stani is that the OP's lodging is on the South Fringe of Fira Town, thus quite a way from Imervogli.

Thanks, jan. I didn't know where they are staying.

However, Imerovigli is definitely worth a visit, to access that gorgeous caldera walkway. Especially when it is lit up at night. Most romantic place ever, from the center of the caldera.

Cabs are cheap.

Thanks to both! Appreciate the insight on the hike, as well as the cabs - have been looking at that info just today.
Is the caldera walkway easy to find?

Yes, it is easy to find. Or just ask anyone.

We live in Colorado, so I don't consider it a "hike" per se. It's a wide, paved, lit walkway.

From Fira to Oia, it's quite long.

We walked from Imerovigli to Fira a few times. There are restaurants, wine bars, and little boutiques all along the way. With hotels cascading up and down the hills. It's the Santorini you see on postcards. I took sooooo many pictures.

I recently had back surgery, and had no problem walking to Fira, but we did take a cab or a bus back to Imerovigli.