The flight is just under 1 hour.
There are 3 direct flights between Kalymnos and Athens every week.
The flight number is GQ31 and it's operated by Sky Express.
From Kalymnos you will fly out from Kalymnos Island (JKL) and you will be landing at Eleftherios Venizelos Intl (ATH).
ATR 72/42 flies this route operated by Sky Express.
Sky Express have non-stop flights to Athens.