There are actually 5 AZ flights from AMS; 3 to LIN, 2 to FCO.

Checkin is handled by KLM; Departures 1, rows 6-8.

As such, the check in desks are always open; but whether KLM will take your AZ bag so early is another thing. It probably helps that you have status/check-in at the Sky Priority area (assuming that the lounge you meant was the KLM lounge, and that you have Skyteam status, rather than a paid lounge you arrange yourself).