The Syriacs are Oriental Orthodox, not Eastern Orthodox. What I said earlier pertains to how we Eastern Orthodox celebrate the Liturgy of St. James on those rare occasions when we do (usually only a seminary or a monastery and even then usually only once a year on the Feast of St. James, if it is celebrated at all. (Remember there are only a handful of Eastern Orthodox who celebrate this ancient Liturgy anymore.)
Since the Syriacs are Oriental Orthodox, they do not follow the liturgical traditions that we do. Many of our liturgical traditions come from Constantinople. The Syriacs follow an older tradition that comes from Antioch. I do not know how similar their version of St. James would be to the Byzantine version we would use. It might be very different, I just don't know. If they were to serve it in its FULL form with no abbreviations it could easily last 3.5 to 4 hours. However, since the Syriacs use St. James as their primary Sunday liturgy, it might not take that long. They could have developed an abbreviated manner of serving it over the years and leave the full , unabbreviated version for the monasteries.