The Friday before Easter.
The mourning period starts at 12 noon and goes until 3PM. During this time the Christian prays and lights candles and remains quiet. No meat is to be eaten. Some Christians fast all day.
On the first day of the Festival of Unleavened Bread, when it was customary to sacrifice the Passover lamb, Jesus’ disciples asked him, “Where do you want us to go and make preparations for you to eat the Passover?” Mark 14:12
Naturally the (Word of God) Gospel of John states that the last meal was before the Passover festival had begun. The Gospel of John makes no explicit mention that the Last Supper was a Passover meal and presents the official Jewish Passover feast as beginning in the evening a few hours after the death of Jesus (special Sabbath starts at sundown).
It was just before the Passover Festival. John 13:1
Now it was the day of Preparation, and the next day was to be a special Sabbath. John 19:31
Because it was the Jewish day of Preparation and since the tomb was nearby, they laid Jesus there. John 13:42
This states that the meal was the day before Passover (he dies on the time of the Passover lamb sacrifice chapter 19). Also at the meal no breaking of bread and no cup of wine symbolizing his blood poured out.