It seems all the planes are released while we are asleep
No they aren't. It is random and frequent. (can it just be that you guys are awake at the same time and grabbing the planes from the market instantly? ..making it look like "there are no planes")
..just a few entries from the log of this game world about a/c market update (though from daytime; my time; but it's the same all the way 24/7). Frequency of updates depends on the number of players and game world "age" (=days from world start; at beginning it's more frequent).
And before anyone tries to look at the times and make out a pattern ... I can save time and say that you can't; it's random (between a defined maximum and minimum update interval; which both again depend on the game world age and player count). Roughly it's between 5 minutes and 3 hours between each update.