When does transubstantiation take place in the Divine Liturgy?
Concerning the moment of “transubstantiation,” Eastern Catholic theology does not narrow in exclusively on the words of institution as being the moment of consecration. The Eastern Church Fathers taught that the Eucharist mysteriously becomes the body and blood of Christ sometime during the anaphora (Eucharistic prayer). Eastern Catholics have traditionally placed a great emphasis on the epiclesis, which is the moment in which the Holy Spirit is called down upon the gifts to transform them into the Body and Blood of Christ. In the great Eatern Liturgies, which we still use, the epiclesis comes after the words of institution.
This difference in no way ruptures our communion with the Latin Church. Rather, it highlights what is distinctive about Eastern Christian theology: a heavy emphasis on mystery. We choose to believe that Christ manifests himself in the Eucharist at some (unspecified) time during the Eucharistic prayer. Narrowing in on an exact moment of consecration is not the Eastern style. Rather, we see the coming of Christ in the Eucharist as being a great mystery which we are unable to comprehend.