The holiday working hours for shops and stores during the period leading up to Orthodox Easter started on Thursday, April 6.
According to the trade association of Athens the proposed working hours for Athens’ stores during the Easter holiday season, is as follows:

Thursday 6 April: 09:00-21:00
Friday 7 April: 09:00 – 21:00
Saturday 8 April: 09:00 – 18:00
Sunday 9 April: 11:00 – 18:00
Monday-Thursday 10-13 April: 09:00 – 21:00
Good Friday: 13:00-19:00
Holy Saturday: 09:00-15:00
Stores will remain closed in Athens on Easter Sunday and Monday.

Source: amna.gr