RS Greece Tour - places to add & timing before/after

If you go after the tour, I think I would look at Crete. For mid September, I would feel fairly confident going to any island given your interests. I don't think it's much of a problem because I would not want to go in summer, and May can be a tad chilly (late May was wonderful on the mainland).
How much time will you have for the island portion? Don't discount the mainland--just my 2c but it's a large country with so much to offer!

We’re retired, so there isn’t a set number of days. But, I know my husband’s internal clock will be ticking to get home (which is fine), so probably five days plus the RS tour. I want to be in Europe longer, but I would like us to discover Greece together, so I will start in another country for a couple of weeks, first.

Ah, not sure I'd do two islands in five days, but we all have different travel tolerances. If you are up for the flight, five days would give you time to see the Minoan ruins in Heraklion, zip over to pretty Chania for the remainder, then fly back to Athens. But others will say not to go to Crete for such a short time.
A very popular itinerary is to get a quick peek at Santorini just to have a caldera on your list, then head to Naxos for the remainder.
One of the posters more well versed in the Greek islands will chime in shortly I'm sure!

We did this tour in October. We thought it was still hot, but not too hot. Unfortunately, we did not have time for any other island besides Hydra. Loved the tour!

It may not be possible for a question of organization but since you plan to go to Italy before Greece, think of Corfu.
It's halfway between Italy and Athens.
And guess what, there is a golf course in Corfu.

Anyway, 2 islands in just 5 days, it's a cruise style journey. If that's your style, why not. But if you like to rest and enjoy a place go only to one island.
If it's 5 full days, Crete is still possible.

And guess what...there are 2 golf courses in Crete!

JoLui, the golf clubs will definitely not be coming on this trip! : ) The only European trip where he wants to be playing golf is when we go to Scotland.

@AMann, yes, I would like to hear more details! I will be in Italy again and miss our September travel group meeting, but I should be there for the rest this Fall/Winter.

Sep 28–Oct 11 is already filling fast - 3 seats left as of now. We booked that tour when it was first offered several weeks ago.

We have been in Greece mid to late September and into October. It will be warm.
Go to Santorini to see the caldera and visit Akrotiri. It is very over touristed and I felt like I had left Greece while there. We have been there twice and will not return. We only went back when Akrotiri reopened to visit it. Three nights maximum.
You don’t have enough time to add Crete. We spent two weeks in western Crete.
To get a better feel of a Greek island Paros or Naxos would be good choices. The Peloponnesean Peninsula is filled with antiquities and plenty of interesting cities and towns to visit. Napflio is only a two hour drive from Athens, one of our favorite places in Greece.
Give Athens four nights so you have three full days to see it’s sites.

Jean, you are in luck - the Sep 28–Oct 11 tour is no longer showing "filling fast" - several people have canceled!

@Silas, thank you for the current status of that tour capacity!

@Silas, it’s showing “waitlist” now for that date.

@Jean, I'm sorry, it flipped to wait list so quickly. The status changed 3 times within such a short time. I wouldn't hesitate to sign up for the wait list considering how often people will reconsider their reservations. I did notice Sep 23–Oct 6 is still free but may be too early for you.