Days spent in Santorini

The vast majority of tourists come to Santorini to see the main "attractions" they have seen in pictures everywhere.
If you are in this case, 3 days will be more than enough.

You can also stay there twice as long if you want to better explore the island, its villages, its wineries (a good idea after Oktoberfest...)

But 9 days, I think that's a lot.

I won't say more, I'm sure "Naxos" will soon appear in the next answers...

No, just relax and see the wonderful houses of Fira and Oia, swim in vulcanic water, visit the ancient Acrotiri, have a hotel with wonderful view (or in Karterados for 1/5 of the price) and taste the delicious wine.

It really depends a lot on your travel style. If you like to relax and get into the rhythm of your destination, 9 days will go by a lot faster than you think. There's plenty to see and do there. https://www.tripadvisor.com/Attractions-g189433-Activities-Santorini_Cyclades_South_Aegean.html

I think 9 days is a lot. Santorini hotels, esp. those with a view, are super $$$.

I suggest you combine this with a trip to another island, for 4-5 days. I highly recommend Paros, to get away from the crowds.

Omg no! Two to three days is more than enough on this volcanic island of massive crowds and no good beaches. Stay a couple of nights, look at the caldera and then get the heck outta there. Go to Naxos, Paros, Folegandros - any other island in the Cyclades! This is a no brainer.

9 days seems like an AWFUL lot unless your goal is just to sit by the hotel pool, and walk around the villages shopping and eating and enjoying life. But if that were my goal, I would not do it on Santorini, which is far too crowded, often with young drunk partiers from England and Germany, to be very relaxing. I would do that on Folegandros or Anafi or Naxos or Spetses or Skiathos, any of the dozens of quieter islands. For me, Santorini was barely worth the 3 days we spent there.

We were just in Santorini (June) and while it is stunning, I thought three days was enough. We were able to walk around, shop, and take a private tour for 1 day around the island. I did not feel rushed. I think maybe you could go 4-5 days, but after that move on or, do what we did, 3 nights in Santorini, then 4 nights in Naxos. It was perfect for us. Also, I think if you don't get a hotel with a view you will be missing out. One of our most special moments for us was eating breakfast on the terrace overlooking the Caldera each morning and then watching the sunset in the evenings without the crowds.

That is way too much time for Santorini! We have been there twice and recommend two nights, three at most. We couldn’t wait to leave on either trip and will never return!
Then go to a different island like Paros or Naxos for a more Greek experience. Better yet, go to beautiful Napflion on the Peloponnesean peninsula or to lovely Chania, Crete.

We were there in October and it has the most beautiful views of anywhere I’ve ever been! That being said, we stayed two nights at Lithies Traditional Homes and I wish it had been three nights. I can’t imagine staying more than that unless you want to just relax on the terrace and enjoy the view. You will love it there. Have a great trip and enjoy Oktoberfest, too!

We spent four nights at Lithies Traditional Homes and it was the perfect amount of time. One day was spent on a snorkeling & catamaran tour around the caldera. Another day we had a private tour of the island and a wine tasting/lunch. The third day was walking around Firostefani and then late afternoon and dinner in Oia after the cruise ship tourists departed. Wine and sunsets on our terrace at Lithies were magnificent!