If you land at the same time as a PIA flight, you could be in for a very long wait. Other times, there are very few people in the queue for non-EU immigration.

On some flights from FRA and AMS half the plan has been part of a non-EU tour party - that would lead to some delays!

You could be through in 10 minutes, or it could indeed take you 90 minutes to get through. If you need to make plans, allow 90 minutes and be happy if you get through in less.