The Pentecostarion provides the feasts from the Sunday of Pascha, to Pentecost, through All Saints – the Sunday after Pentecost.
Bright Week, from Pascha till the following Saturday, is fast-free and only the Synaxarion of the Menaion is used daily.
On the Monday after Thomas Sunday, we resume using the hymns of the Menaion daily with those of the Pentecostarion.
On the Monday after All Saints we begin the Apostles’ Fast.
Since the Apostles’ Fast begins the day after All Saints, its beginning is based on the moveable Paschalion. But its end occurs with the feast of the Apostles Peter and Paul, June 29, which, unlike the moveable feasts of the Pentecostarion, is an immovable feast of the Menaion: at this point the moveable Paschalion meets the immovable Menaion.