Originally Posted by
Perche
It's a 24 hour that is always operational. When KLM staff show up behind the counter and become operational is dependent on how KLM operates, not on how the terminal or airport operates, because it's operational 24 hours. Most airlines have their staff behind the counter and ready to start doing things an hour before the flight, but there's a margin of error around that.
It is my experience that every airline, at every airport in the world, has check in agents on duty at least 3 hours before each flight. Of course, this might be because I am usually flying into or out of Israel or the United States and they want extra time for security but even on intra-Schengen flights I have been able to check in 3 hours early.