Are all divine liturgies about two hours? Does the time differ by church (Romanian vs. Greek vs. Antiochian)?
Do they differ for holidays?
The Sunday liturgies tend to be longer during Lent. During Lent we celebrate the Liturgy of St. Basil on Sunday, while we celebrate the Liturgy of St. John Chrysostom on Sundays outside of Lent. The prayers of consecration are significantly longer in the Liturgy of St. Basil.
Another factor that often has a significant impact on the length of the Liturgy: whether the priest preaches a homily or not. The homily itself can make a Divine Liturgy anywhere from 10-30 minutes longer.
As for feast days, my experience is that the Vesperal Liturgy the eve of the feast (officially prescribed only for the eves of Christmas, Theophany, and Pascha, and for the evening at the end of the Feast of the Annunciation) is often VERY long with as many as 8-15 Old Testament readings (8 for Christmas, 12 for Theophany, and 15 for Holy Saturday). The Liturgy of the Eucharist for a Vesperal Liturgy is also according to the Liturgy of St. Basil, which only makes it that much longer. For the day of the feast itself, however, the Liturgy can be very short. The hymns tend to be joyously quick, there aren't that many of them (especially the Troparia/Apolytikia and Kontakia), the prayers are those of St. John Chrysostom, and--at least in my parish--the priest doesn't preach a homily if the feast is on a workday.