At the moment the defensive side gets to choose a window for priority but they can still drop during inactive windows. Thoughts on doing sieges like this.

Server (or clan) has a specific window.
Offensive clan sieges
Defensive clan has 18 hours to choose the time it goes live withing their window.
Siege goes live 2 days after drop instead of one.

Reason: While Defensive can choose inactive window, they can still be dropped on at bad times and currently Offensive gets the advantage for choosing the time it goes live. Let that be in the Defensive sides hands.