Then they tweaked them again and made hours 8:00 to 8:00 for certain kinds of multi-national concerns and all supermarkets on Mondays, Wednesdays and Saturdays. However, these rules never applied equally to Pharmacies which are closed on Saturdays and Sundays except for emergency ones in each neighborhood. Pharmacies have their own Byzantine system of hours so if you see one open: shop. If you see one closed, they are required to have a list in the window of other pharmacies that are open, when and where. The newspapers also have lists which are often wrong, even on line. I know from personal experience. So call in advance and make sure they are really open.
So now you had to remember what day was what and what business was open what time and what day.
Of course this never applied to Banks and Government Ministries and the interminable transition from the Old Greece to the New Greece has changed nothing for them, they still close at 1:30 pm. There are automated tellers for banks at least, in parts of the New Greece and mail boxes for those that buy stamps for their home country all at once.
Greek Post Offices and banks aren't just places to mail things or deposit money, however. They offer Greeks the convenience to pay other state or quasi-official type bills such as taxes and state run insurance, phone, water and up until very recently, electric bills. Expect long lines at banks and at the busier Post Office's, really long lines.
As you wait in these lines, sometimes sitting, sometimes standing, you'll be glad you took a number from the dispenser as you entered. Exactly like a deli service number back home at the super market or bakery. Look around for the dispenser, its usually near the entrance but can be blocked by large crowds or potted plants.