Kardamili is at its best in spring (April to early June) and autumn (September to October). The weather is warm but not overwhelming, the village is relatively quiet, the Viros Gorge is at its most beautiful — the stream running, wildflowers out in spring, the plane trees golden in autumn — and you can walk and swim without the crowds of July and August.
July and August are busy. Greeks on holiday fill the tavernas and the beach, prices rise, and the village loses some of its quietness. That said, the surrounding landscape absorbs the crowds reasonably well, and the evenings remain pleasant.
Winter (November to March) is very quiet — most tavernas close, accommodation is limited, but the village and coast have a melancholy beauty and you will have the gorge entirely to yourself. The Mani is famous for its microclimate; it is often warm and sunny when the rest of southern Greece is grey.