Handbook of ROCOR Liturgical Practice:

At what point in the Divine Liturgy is a homily given, and how is it offered?

While there are no formal rubrics that place a homily at a specific place in the Divine Liturgy, the custom in the Russian Orthodox Church is for a homily, when offered, generally to come in one of two places: either immediately before the communion of the faithful (i.e., after the Priest has communed himself in the Holy Altar and prepared the Lamb in the chalice, before opening the Royal Doors to commune the people), or at the end of the Divine Liturgy, before the benediction (when offered in this place, the choir sings the usual ‘Blessed be the Name of the Lord…’ twice, and then the homily is offered; as soon as the homily concludes, the choir sings the third and final ‘Blessed be the Name of the Lord…’, and then the Liturgy concludes as usual).

The presiding Priest may choose to offer the homily in either place, as he wishes. When a Bishop serves, by custom he will always preach at the end of the service.

Wherever the homily is offered, it always begins in this way: The homilist preaches in full vestments (that is, the Priest puts back on his kamilavka / head covering if awarded it and it is otherwise off at the point in the service when the homily is offered, and preaches with it on), and begins always with the words: ‘In the Name of the Father, and the Son, and the Holy Spirit’ without either he or the people saying ‘Amen’. He then offers his homily, and only at the end of it does he say ‘Amen’ — that is, the entire homily is offered in the Name of the Holy Trinity, and concluded with a final Amen.