According to the Schiphol site The Panorama terrace opening hours are:
* Winter period (from the last Sunday in October) from 09.00 hours to 17.00 hours.
* Summer period (from the last Sunday in March) from 07.00 hours to 20.00 hours.
So I hope you will be at AMS after the last Sunday of March...
June 18th is a saturday, so most likely there will be other (Dutch) spotters around to drive you to the runways. If you are into photography, those are the better places to go. If you post this message again early June I will see if I can attend. Might go to the Paris Air Show then, so can not give any guarantees yet.