The thing with Via Ferrata routes is how long you take often depends on the size of your group, their fitness, and how comfortable everyone is with heights and using their gear.
I've seen people at a crawl on some simple via ferrata lines that provide some assistance on high exposure parts of popular hikes. They have both hands on the cable, bodies as low as they can get them and close to the rock, terrified of the drop to their side, while others would comfortably walk past them without even touching the line.
Not everyone is going to do the route in the same amount of time, you need to take the average and apply that to your level of speed and fitness, but you also need to factor in the possibility of traffic jams, you could get stuck behind a slow group. If I were you, I'd give myself a lot of extra time, get an early start, plan on somewhere around 4 hours and see how you do.