The entire celebration of the Easter Vigil must take place during the night, so that it begins after nightfall and ends before daybreak on Sunday. 

The Mass of the Easter Vigil, even if it is celebrated before midnight, is a paschal Mass of the Sunday of the Resurrection, and fulfills the obligation to attend Mass on Easter.  Anyone who participates in the Mass of the Easter Vigil may receive Holy Communion again at Mass during the day on Easter Sunday.