It all depends on how many people are taking it with you and how many examiners are there. If you have a small group you can fly through there, but most places are doing larger groups because they have to pay the testers and it gets expensive if they don't have a larger pool of students.
When my classes tested we usually were in with another class, so we had 35 - 45 people. We were generally done by 1:00 pm but they also had a lot of testing stations. Depending on how they organize it you may end up having to wait for a single station (assessment is usually the pinch point).
