During the recent Season of Discovery Phase 4 Preview, the developers stated that all endgame raids would reset on a bi-weekly lockout schedule. However, after considering community feedback on the topic, the developers have decided to keep a bi-weekly lockout cadence for Onyxia's Lair, Lord Kazzak, and Azuregos, but change the Molten Core lockout to a weekly schedule.
Molten Core will utilize the standard 7-day lockout period, based on your feedback.
We will be keeping the Twice-Weekly lockout in place for Lord Kazzak, Azuregos, and Onyxia, however. We feel that those quicker, single-boss raid encounters feel appropriate for this interval, especially considering that Onyxia herself operated on a 5-day lockout timer throughout Original WoW.
As always, we appreciate your feedback on this topic and will continue to evaluate things and listen as we move through the content phases and make additional adjustments as necessary.
The team is really looking forward to having you join us in Phase 4 in just a few short weeks!
Thank you!
-The WoW Classic Dev Team.