The answer
Between seven months to one year. It is preferable not to extend the engagement for longer than a year, for when the engagement period is prolonged, problems may start to occur.
H.G. Bishop Moussa
H.G. Bishop Moussa · Youth Concerns · 109
Faith Q&A › Youth Concerns › Relationships and Marriage
How long should an engagement period be?
H.G. Bishop Moussa, Bishop of Youth, Youth Concerns (Questions & Answers). Compiled by Lisa Agaybi. Coptic Orthodox Patriarchate, Bishopric of Youth Bookstore.