The tourist season in Santorini typically starts in April, and runs through to the end of October. This is when the weather is the warmest and the majority of the island’s tourist attractions and beaches are open for visitors. The peak of the tourist season is from June to September, when the weather is the warmest and the beaches are the busiest.The best time to visit Santorini for relaxation would be during the shoulder season, which is typically in April, May, September, October. During these months, the weather is still pleasant and the crowds are smaller. The island can offer a more relaxed and peaceful experience during this time, with fewer tourists and more availability of accommodations. The water temperature might be a bit colder though.The most favorable months to visit Santorini are from late april to early October, with peak season being July and August. This is when the weather is warm and sunny, making it ideal for outdoor activities, sightseeing, and beach activities. June and September are considered the shoulder months and can offer a good compromise for those seeking fewer crowds. Winter months can be cooler and damp with limited tourist activity.
If you want to enjoy the views of Santorini with fewer people, stay in the pool and not get too hot, I recommend that you come in April and May, in April the hotel prices are lower.
And if it is very important for you to spend a few days at the sea at the black sand beach in Santorini, I recommend you to come after September 15- October 10, after October 10 the weather cools down and sometimes rain is possible, but you can also catch good days
Officially, the end of October is also considered the end of the season