Hi dclarke - I went to Kardamena from 3rd October for a week about 4 years ago, and apart from one evening (about 7) of about 30 minutes of rain which soon dried up - the weather was perfect. It is absolutely warm enough for sunbathing all day, and actually, less cloudy than in the Summer when we've been (been 4 times so far!). I would say that in the evening it is a little cooler (but my husband prefers that as he sweats too much at night in the summer with jeans on!). I would recommend long-sleeve tops at night but then again, i'm nesh!!
Enjoy yourself. Incidentially if you are going to Kardamena, do go to Gianni's (best restaurant on the island) and have a meat mezze for two - it's the most delicious thing we've ever had!