konagirl2 is basically correct, AMS refers to these colloquially as "night slots" and they are tied to the IATA seasons (winter / summer). For this IATA winter 2017/2018, Delta's night slots belong to 160 MSP-AMS, 132 DTW-AMS and 46 JFK-AMS.

If it's already a "night slot" flight, there's no problem landing early. If it's a "day flight" (not one of the above 3 listed), you can't land earlier than 710A local or you get fined. It's not a hard curfew per se, but they will delay up-line to make sure the 710A landing time isn't busted. This is why DL132 was able to blast off, and got to the gate in AMS before 5am, but DL134 took the delay.

random cool link if you want a graphical depiction of what the winds are doing right now (it's kinda mesmerizing in a dorky way ). Under "height" click 250mb for winds at 34,000 feet

https://earth.nullschool.net/#curren...4.90,38.31,814