When do Orthodox Christians celebrate St. George?

Name day celebrations are important affairs for Orthodox Christians, often being more auspicious than birthdays. George was always a most popular name for Greeks. Celebrations that coincide with the Great Lent or the Holy Week, such as St. George's Day or St. Mark's Day, are moved to the Sunday before Easter  Sunday, or the week after Easter Sunday.

This is because during Lent from Sunday afternoon to Friday morning Orthodox Christians have a period of mourning. So there are no celebratory celebrations.

So this year with Easter on 8 April the memory of St. George is celebrated on April 23rd.

It must be noted that the liturgy honoring Saint George was written before the change of the calendar, and at that time the feast always fell after Easter.