Don’t worry about it too much. I had my interview last week and was told it would be 90 minutes and it did last about 75 minutes but the reason it takes so long is that they have to write down all of your answers. As everyone says I was asked to give 2 examples of each competency and I got asked a few questions around each example e.g. what did you find most challenging about this etc. But I think they only ask these more in depth queries to make sure you answer the questions thoroughly, and give you the best opportunity to pass. I also got the opportunity to ask them questions. My interviewer was really nice and the interview was quite relaxed.
One tip I would give is to think about how some of your examples for competencies can be adjusted for different situations. I was expecting to be asked: Can you describe two examples of when you have shown good communication skills? when in actual fact my interviewer had thought of two questions based on communication skills. i.e. Can you describe a time you’ve had to explain something to someone? This wasn’t a big problem but it did mean me having to adjust some of my examples at the last moment.
I got through to the next stage btw!