Here is my experience:
I arrived in plenty of time, and asked a KLM rep if I needed to check in. Passengers DO need to visit the check in desk to get a boarding pass, even if they have checked in online and printed a boarding pass. I asked the check in agent if they really close check in 2 hours before departure, and she said no it's just to try and get people there on time.
Immigration and security took less than 5 minutes each and I therefore had a very long wait in the nice new Akwaaba lounge.