8 nights in Greece - Enough time Santorini & Naxos?

Depends on the experience you want , Athens is one of my least favourite cities in Europe,however there are amazing sites there .
Personally I think girls would love santorini and Naxos more , so one full day in Athens would be enough for me .

That is really a VERY short trip to Greece -- But you'll just have to return again. Hope you have a flight from Rome that gets to Athens before mid-day (you don't say). It gives you more options on flights to Santorini. 2.5 days in Santorini is Ample -- since the beaches there are not what your teens will want .... get a hotel with a view of the Caldera, but the beaches are way on the other side of the island and are black & gritty. If you can swing it, go for a hotel with a pool. Yes, take that 3:30 Blue Star ferry to Naxos, buy economy seats, sit on deck, have a nice "mini-cruise."

YOur problem is, you want more time in Athens, but don't want to give up a day in Naxos. You have an option -- instead of taking that Wednesday 9 am ferry that eats up the whole day, take the 6 pm ferry (I call it the "sunset sail." You'd have to check out of your Naxos hotel at noon, but hoteliers will gladly stash your bags in their luggage room -- and if you ask nicely, they'll have a spare restroom available for you to "freshen up" before your ferry. You then can have a relaxed afternoon at the beach, or shopping in town, then about 4:30, come back, wash up & change into travel clothes & head for the dock. BTW, since your stay is short, stay at St. George Beach, it's directly adjacent to town, you can walk it in 15 mins or so. Villa Naxia is a great place at far end of beach, has units with separate BR (some have 2) and kitchenette & 2 daybeds in main room + balcony ... right off the sand, not crowded even at end of June. BUt bookearly! It's always in demand.

A couple of days before sailing Buy "reserved economy" seats (otherwise known as "aircraft seating"). YOu can sit on deck until dark if you like, but when you want to snack, read, snooze, this means you have an indoors reserved seat -- upholstered, lean-back, roomy. Taxi to your central Athens hotel, in bed by 1 am. If you can drag the girls out of bed early on Wednesday AM you can hit the Acropolis gates at 8:30 .... to beat the crowds. If not, then see other stuff in the day, and go to the Acropolis afte 4 pm... the crowds will be gone and it won't be so hot. Then you'll have all day Friday also.

It depends on what kind of trip you want. If you want a "city" trip then, there is not enough time for Athens. We did three days in Athens last year and that was enough for us. We followed that up with four full days in Naxos and that was amazing but our vacation was about islands and beaches and not so such about seeing Athens. We did a day trip to Mykonos from Naxos and 3 days in Naxos was fantastic but we were looking for a casual beach vacation. We followed up with days in Santorini and 4 days in Crete. I love Santorini and my teenage daughter thought it was one of the most beautiful places that she had even seen but I don't think that was the best place for our family vacation. She was ready to go at end of day 2 and so was my son (9 years old). They found it dull other than the scenery so just two days there like you have planned was ideal. Then you will have two days in Naxos. Not enough, IMO but it could work, but that ferry trip on July 5 is the killer for me. We find ferry rides restful but with only few days I would not waste a full day traveling. That is one of the reasons why we flew between from Athens to Naxos.
Edit: +1 for what Janet said about the beaches. That was exactly our problem -- my kids did not like them. And also +1 for the suggestion of the evening ferry which will definitely get you that extra day in Athens and keep you from wasting a full day traveling.

Of the three desired destinations, at the end of the trip you will be agreeing, that Naxos was the most enjoyable part of the experience.

I might suggest rather than hanging around Santorini for the 1:30 Blue Star take the first Champion Jet 1 which I believe departs Santorini around noon and gets you into Naxos around 1. Its more expensive as it is a fast cat but it does have an open deck at the back so you can be on the deck for departure from Santoirni which is spectacular.

This way you are checked in your hotel in Naxos before the blue star even departs Santorini. Time is more valuable than money on a short vacation. Champion Jet is the way to go in your case.

The first few images of our Naxos visit this year were taken from Champion jet 1 back deck departing Santorini
https://www.flickr.com/photos/stanbr54/sets/72157671589993576
Plus
Naxos Town http://www.flickr.com/photos/stanbr54/sets/72157632094558042/
Trip around Naxos http://www.flickr.com/photos/stanbr54/sets/72157634605629689/

Thanks to all who replied with opinions & suggestions.

I just discovered Olympic Air has a promo airfare Naxos to Athens (only in one direction), 3X daily <$24 per person. This is much cheaper than the ferry. I wonder how long the promo will last while I coordinate my other flights/plans? Do I need to act quickly? At least this helps me determine which order to do the islands as long as the FCO - JTR leg is reasonable.

Interesting, I got the sense from others that 2 days in Santorini is about the right amount of time. With that in mind I will lean towards more time in Naxos.

6/29 fly from Rome straight through to Santorini (earlier the better) - 2 nights Santorini
7/1 ferry to Naxos @ 3:30pm (gives final 1/2 day+ in Santorini) - 4 nights Naxos
7/5 fly to Athens @ 11:40am (gives additional 1/2 day in Athens) - 2 nights Athens
7/7 fly home @ 12:30pm (breakfast in Athens before taking bus to the airport)

Thanks
Bret

Bret that looks darn good to me!! If you get the "semi-flex" ticket that allows you to switch flights without penalty (in case of some major change you don't know about at this time) ... Also I totally agree with Stanbr about the Champion Jet, that boat with the open back-deck didn't use to be available. That way, Santorini is All About the View for your family, and Naxos can be about beach & Old Town enjoyment. You might even rent a car for a half-day or more, to zoom around the island, if you like.

One of the reasons (besides the beach) that teens always vote Naxos their favorite ... it's so easy & SAFE for teens to be relatively on their own, especially if you stay at St. George (Ag Giorgios) beach. They can meet lots of others their age on the beach (and most of the European ones speak some English), they can wander into town to hang out at THE teen meeting-place, an Ice-cream palace, The Waffle House, etc etc. U can always send them with a phone so u can be in touch when it's time to reunite, but they can enjoy more independence without being constantly within sight. At that age, alas, being with parents is so ewww. PS: It means the parents can get a break from them too!