Even before and after Mass. From the General Instruction of the Roman Missal, n. 45:
“Even before the celebration itself, it is a praiseworthy practice for silence to be observed in the church, in the sacristy, in the vesting room, and in adjacent areas, so that all may dispose themselves to carry out the sacred celebration in a devout and fitting manner.”
From Ceremonial of Bishops , Part II Mass, Chapter 1 Stational Mass of the Diocesan Bishop, in the section headed “ Concluding Rite”, n. 170:
“When they reach the vesting room (sacristy), all make a reverence to the cross together with the bishop. Then the concelebrants bow to the bishop and carefully put away their vestments. All together the ministers also bow to the bishop, then lay aside the articles they have used in the celebration and their vestments. All are to be careful in observing silence, out of respect for a spirit of recollection and the holiness of the house of God.”
[Excerpt from the English translation of The Roman Missal , © 2010 International Commission on English in the Liturgy Corporation. Excerpt from the English translation of Ceremonial of Bishops , © 1989, International Commission on English in the Liturgy Corporation. All rights reserved.]