For the Athens Airport, there is a 24-hour operation. The same goes for the 2021 summer period for Fraport GR Airports. (http://www.hsca.gr/coordinated_en.html)  As for HCAA Airports, their operating hours are determined for the period from 28 March to 30 October 2021 (see relevantly: http://www.hsca.gr/assets/files/S21_HCAA_OPHRS_PARAMETERS.pdf ). See also: http://www.ypa.gr/userfiles/4659ed30-b59b-4111-9747-a3550129731a/%CE%A9%CE%A1%CE%91%CE%A1%CE%99%CE%9F.pdf