the liturgical season of Lent ends at sundown on Holy Thursday, when the Mass of the Lord’s Supper begings (actual time set by each diocese). This begins the liturgical season of the Triduum, 3 days, sundown Thursday to sundown Good Friday, sundown Good Friday to sundown Holy Saturday, when the Easter Vigil begins (time set by each diocese), beginning of Easter Vigil to midnight Easter Sunday, third day.
the Paschal Fast begins after the Mass of the Lord’s Supper, when the Body of the Lord is removed from the tabernacle and processed to an altar of reposition in another suitable location, in a silent procession, for adoration by the faithful, not to extend past midnight. This should be a more intense, deeper fast than the Lenten fast, not only from food, meat etc., but from frivolous pursuits in general, and should be as much as possible a time of silence, necessary speech only. This of course is intended for the Elect who are preparing most intensely and are in retreat in anticipation of their sacramental initiation, but by extension, the whole Church should be fasting. Definitely not the time for parties and entertainment. This fast ends when the Easter Vigil begins.
yes, for those who ask, in former days vigils of great feasts like Easter and Christmas were days of fast and abstinence. Sunday has never been a suitable day for fasting, because the gospel tells us, we do not fast when the Bridegroom is present.
notice that the penitential color of purple is lifted on Holy Thursday, as the altar is clothed in white, and stripped after the conclusion of the liturgy