Mid-season sales start on May 2

The newly-established mid-season sales, including one optional Sunday on May 4, will be held from May 1-10 based on new laws passed in 2013. Given that May 1 is a mandatory bank holiday, this effectively means that the sales period will start next Friday, May 2.
Shops can also choose to stay open on May 4, the first Sunday within the sales period, for a maximum period of 11:00-20:00.
In an announcement on Monday, the Piraeus Merchants' Association has proposed that its members in Piraeus open from 11:00 until 16:00. The Thessaloniki merchants' association also informed its members about the optional Sunday opening on May 4 and vendors' obligation to inform customers of both the old and new prices, in addition to the percentage reduction offered, on price tags.

source: ΑΜΝΑ