Both are situated on the main street of Antiparos town (chora) as you go up the street on the left hand-side.
Opening times for Alpha bank are 08:30 to 14:00 Monday to Thursday. Branch opened for summer on the 19th of June, 2017.
Opening times for Ethniki bank are Monday 08:30 to 14:00, Wednesday 08:30 to 14:00 and Friday 08:30 to 13:30. Branch opened for summer on the 7th of June, 2017.
Update 25/7/2017: Ethniki bank is now open daily Monday to Friday.
Both banks are closed on Greek national holidays (e.g. on Tuesday the 15th of August, 2017).
Both banks have ATM machines outside of the branches where you can withdraw cash with widely used credit cards (e.g. Visa, Mastercard, etc.) 24 hours per day.
There two more ATM machines at Antiparos port from Piraeus bank and Eurobank.